More than two years after the City of Chicago (the “City” or “Chicago”) agreed to discipline and discharge its firefighters solely for cause, the City adopted a Mandatory Retirement Ordinance (“MRO”) compelling firefighters to retire at age 63. Two of the firefighters who were forced to retire under the MRO filed suit on behalf of themselves and others similarly situated, contending that mandatory retirement amounted to age discrimination prohibited by the Age Discrimination in Employment Act (“ADEA”) as well as a deprivation of procedural due process. We concluded in
Minch v. City of Chicago,
*297 I.
On January 14, 1998, the City and its firefighters entered into a collective bargaining agreement effective for the four-year term beginning July 1, 1995 and ending on June 30, 1999. More than five years later, on July 9, 2003, the parties entered into a successive agreement governing the period from July 1, 1999 through June 30, 2007. In each instance, following the execution of the agreement, the Chicago City Council enacted the agreement into law. In all material respects, these two agreements were identical, and for ease of discussion we shall henceforth treat them as a single agreement (the “CBA” or the “agreement”). We set forth the relevant terms of the agreement below.
ARTICLE IX
SENIORITY RIGHTS
Section 9.1 Seniority
A. Seniority is defined as an employee’s length of continuous service since his last date of hire....
C. An employee’s continuous service and the employment relationship shall be terminated when an employee:
1. Resigns or quits ...[;]
2. Is discharged for just cause;
3. Retires or is retired;
4. Is absent for three (3) consecutive days (workdays) without notifying the Employer’s authorized representative;
5. Is laid off and fails to report for work within ten (10) calendar days after mailing ... a notification of recall ...;
6.Does not report to work after the termination of an authorized leave of absence,....
ARTICLE XIII
NO DISCRIMINATION
Section 13.1 No Discrimination
... In accordance with applicable law, neither the Employer nor the Union shall discriminate against any employee covered by this Agreement because of race, creed, color, national origin, sex, age, religion or political affiliation.
ARTICLE XVI
GENERAL PROVISIONS
Section 16.2 Discipline and Discharge
B. The Employer agrees that employees shall be disciplined and discharged only for just cause....
ARTICLE XIX
GUARANTEE OF TERMS
The Employer agrees that this Agreement shall be immediately submitted to the City Council of the City of Chicago for ratification and concurrent adoption in ordinance form pursuant to the City’s Home Rule authority. Such action by the Council shall commit the City of Chicago to enact no subsequent ordinances, executive orders or rules and regulations having the force and effect of law which would impair the binding *298 effect of or make unenforceable the terms of this Agreement.
R. 112 Ex. A.
In the years preceding the parties’ negotiation and adoption of the Agreement, federal age discrimination law had been in a state of flux with respect to age limits on public safety personnel. A more complete history is set forth in our opinion in
Kopec v. City of Elmhurst,
Seventy years ago, Chicago for the first time enacted an ordinance requiring those of its police and fire personnel holding civil service positions to retire at the age of 63.
See Malloy v. City of Chicago,
On December 31, 2000, the effective date of the reinstated age limit, the two named plaintiffs in this action, James D. Minch and Richard A. Graf, were required to retire from the Chicago Fire Department against their wishes. Minch was 64 at that time; Graf was 63.
Minch and Graf
1
then filed suit against the City on behalf of a class of similarly
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situated firefighters contending, among other things, that enforcement of the City’s MRO violated the ADEA and deprived them of their Fourteenth Amendment right to due process.
2
After the district court (Hon. Elaine E. Bucklo) denied the City’s motion to dismiss these claims,
Drnek v. City of Chicago,
With the ADEA claim out of the case, what remained was the plaintiffs’ Fourteenth Amendment due process claim. The due process claim is premised on the notion that the terms of the CBA, to which the City had contractually and legislatively bound itself, precluded the City from summarily forcing any firefighter to retire based solely on his or her age and gave the firefighters a protected property interest in continued employment absent good cause to discharge them. Section 16.2(B) of the CBA reflected the City’s agreement “that employees shall be disciplined and discharged only for just cause.” (Emphasis ours.) In the plaintiffs’ view, involuntary retirement amounts to a discharge, and as such was an action the City could *300 only take with just cause — age alone would not suffice. The plaintiffs also construe two additional provisions of the CBA to have precluded the City from adopting the MRO: Section 13. 1, which prohibited the City and the firefighters’ union alike from discriminating against any employee based on age, “[i]n accordance with applicable law,” and Article XIX, which provided that once the CBA was ratified and enacted into law, the City would enact no further legislation nor adopt any rule “which would impair the binding effect of or make unenforceable the terms of this Agreement.”
While the case was pending on interlocutory appeal, it had been reassigned to a new district judge (Hon. Samuel Der-Ye-ghiayan). On review of this court’s decision in Minch I, the court invited the City to re-file its motion to dismiss the due process claim. Judge Der-Yeghiayan believed that Judge Bucklo’s rationale for refusing to dismiss that claim overlapped with her reasons for not dismissing the ADEA claim; given this court’s decision that the ADEA claim was not viable, Judge Der-Yeghiayan believed that a fresh examination of the due process claim was in order. R. 146 at 3; see also R. 133 at 4. The City accepted the district court’s invitation and renewed its motion to dismiss this claim.
After entertaining the parties’ memoran-da, the district court dismissed the due process claim. R. 120;
Minch v. City of Chicago,
II.
The district court disposed of the due process claim pursuant to Federal Rule of Civil Procedure 12(b)(6). A court may properly dismiss a claim pursuant to Rule 12(b)(6) only if the plaintiff could prove no set of facts consistent with the allegations of the complaint on which relief could be granted.
Conley v. Gibson,
*301
At the outset, we may put aside any concern as to whether the district court failed to pay adequate heed to the law of the case doctrine. Among other things, the law of the case doctrine embodies the notion that a court ought not to revisit an earlier ruling in a case absent a compelling reason, such as manifest error or a change in the law, that warrants reexamination.
See, e.g., Santamarina v. Sears, Roebuck & Co.,
*302
Nonetheless, Judge Der-Yeghiayan did re-assess the due process claim and find it wanting, precipitating this second appeal. The law of the case doctrine did not necessarily preclude him from doing so to the extent he was convinced the earlier ruling was obviously wrong.
See, e.g., Brengettcy,
An essential component of a procedural due process claim is a protected property or liberty interest.
See Town of Castle Rock, Colo. v. Gonzales,
The essential question before us is whether the terms of the CBA are properly understood to bar mandatory retirement. The CBA certainly lacks any provision that expressly authorizes the City to adopt a mandatory retirement age. (By contrast, the agreement that the City entered into with its police officers reserved to the City the authority to impose a mandatory retirement age.) But the omission of such a term is not dispositive. The relevant inquiry is whether the provisions that the parties did include in their agreement preclude the City from imposing a mandatory retirement age on its firefighters. If so, they may have had a protected property interest in continued employment beyond the age of 63.
The CBA term on which the plaintiffs place most emphasis is section 16.2(B), which reflects the City’s agreement to discipline and discharge an employee solely for just cause. The City concedes that this provision precludes it from taking disciplinary action against an employee, up to and including firing the employee, without just cause for that action. City’s Brief at 26-27. In the plaintiffs’ view, mandatory retirement is a form of discharge and as such is not permitted under section 16.2(B) absent just cause— which presumably an employee’s age alone would not supply. (“Just cause” is not defined in the agreement, but the parties appear to agree that an employee’s age alone would not constitute just cause to discharge him.)
But is involuntary retirement a discharge for purposes of section 16.2(B)? The answer is not obviously yes. Compelled retirement, like a discharge, severs the employment relationship between employer and employee. Nonetheless, there are intuitive distinctions between being fired and being forced to retire. Retirement is necessarily linked to the employee’s age and/or tenure with the employer; and whether voluntary or not, retirement often bestows certain benefits on the employee (e.g., a pension and/or continued receipt of insurance and other employee benefits) that he would not enjoy if simply fired. (There is the same intuitive distinction between quitting and retiring voluntarily). Being fired and being forced to retire indubitably have in common the fact that the employer unilaterally terminates the employment relationship. But only a broad understanding of the term “discharge” that brings within its reach any and all forms of involuntary termination would demand just cause even for an unwilling retirement.
It is in this regard that section 9.1(C) of the Agreement is relevant. For purposes of assessing an employee’s seniority rights, section 9.1(C) identifies a variety of ways, both voluntary and involuntary, in which a firefighter’s employment relationship with the City may terminate. Discharge for cause is among the identified forms of severance, § 9.1(C)(2), but is by no means the exclusive means of involuntary termination listed. For example, the agreement recognizes that the employment relationship terminates when an employee “retires or is retired.” § 9.1(C)(3). Judge Der-Yeghiayan thought that the “is retired” language was an explicit reference to (and authorization of) involuntary retirement. It plausibly could be so understood, although this reads much into the use of the passive voice and, in the absence of any other contractual reference to mandatory retirement, may place more weight on the *304 phrase than its two words ought to bear. But even if we place the “retires or is retired” language in the category of voluntary terminations along with “[rjesigns or quits,” see § 9.1(C)(1), there remain several other forms of involuntary termination that section 9.1(C) recognizes as distinct from a discharge for cause. These include: being absent from work for three consecutive days without notifying the employer’s representative, being laid off and then failing to report back to work within ten days of being recalled, and failing to report back to work on the conclusion of an authorized leave of absence. § 9.1(C)(4)-(6). This makes clear that the term “discharge” in section 16.2(B) does not include all forms of involuntary termination, such that just cause invariably is required whenever the City terminates a firefighter’s employment unilaterally. We note that a neutral arbitrator came to the same conclusion in resolving a dispute between a terminated firefighter and the City. R. 114 Ex. A (Chicago Firefighters’ Union, Local No. 2 v. City of Chicago, Griev. No. 990133, Decision & Award at 22-23 (Mar. 7, 2000) (Peter R. Meyers, Arb.)).
The plaintiffs retort that section 9.1(C) is a seniority provision that in substance deals only with the question of when the employment relationship terminates rather than how (or, put another way, for what reason) it may be terminated by the City. We have not overlooked the context of the provision. But even having in mind that its focus is the termination of employment for seniority purposes, this section nonetheless is relevant for the light it shines on the scope of the term “discharge.” In recognizing multiple forms of involuntary termination apart from a discharge, this provision puts to rest the notion that any termination against the employee’s wishes is necessarily a “discharge” for which the City must have just cause. Given the distinctions between retirement and discharge, we do not read section 16.2(B) to condition involuntary retirement on a showing of just cause.
The plaintiffs alternatively rely on the CBA’s Guarantee of Terms as a bar to the City’s enactment of the MRO. Article XIX provides that once the Chicago City Council has ratified the CBA and enacted it into local law, the City shall “enact no subsequent ordinances, executive orders or rules and regulations having the force and effect of law which would impair the binding effect of or make unenforceable the terms of this Agreement.” We assume for the sake of argument that Article XIX would preclude the City from adopting a mandatory retirement age if, as the plaintiffs have argued, Section 16.2(B) conditioned all forms of involuntary termination, including involuntary retirement, on the existence of just cause. So understood, the CBA would give a firefighter the right to continue working regardless of his age, so long as he could perform the duties of his job and gave his employer no cause to discharge him. And by forcing employees to retire at age 63, the subsequent adoption of the MRO could be thought to impair the binding effect of section 16.2(B) and/or to render it unenforceable.
But because section 16.2(B) does not foreclose the City from imposing a mandatory retirement age, Article XIX poses no independent obstacle to the MRO. Assuredly, the MRO imposed a new condition on the employment of firefighters to which the firefighters’ union had not agreed. Unilateral though it was, however, the enactment and enforcement of the MRO neither impaired the binding effect of the CBA nor rendered unenforceable its terms, none of which precluded the adoption of a mandatory retirement age.
*305 Nor do we construe Section 13.1’s non-discrimination provision to bar the MRO. This provision of the CBA forbids age discrimination “[i]n accordance with applicable law,” which we understand to define the scope of prohibited discrimination as discrimination which is prohibited by federal, state, or local anti-discrimination law. The Chicago Human Rights Ordinance prohibits age discrimination in employment without an explicit exception, akin to that in the ADEA, for age limits on public safety personnel. Chicago, Ill. Municipal Code § 2-160-030. The plaintiffs thus contend that enforcement of the MRO amounts to a violation of the Human Rights Ordinance.
Yet the same legislative body that enacted the Human Rights Ordinance also enacted the MRO, and in so doing explicitly mandated the age-based retirement of firefighters. The Chicago Commission on Human Relations, in response to discrimination complaints filed by Minch and Graf, concluded that the MRO was reasonably understood as an implicit exception to the Human Rights Ordinance’s ban on age discrimination.
In re Minch, et al,
Case Nos. 01-E-21/44/48,
III.
The collective bargaining agreement between the City and its firefighters did not preclude the City from subsequently adopting a mandatory retirement age. Because the CBA did not give the plaintiffs a protected property interest in continued employment regardless of their age, the plaintiffs cannot show that they were deprived of procedural due process when the City adopted the MRO and enforced it by compelling their retirement at age 63. Accordingly, the district court properly dismissed the due process claim. We need not reach any of the other arguments the parties have raised.
Affirmed.
Notes
. Mandatorily-retired police officer Richard Cosentino joined this suit on behalf of himself and similarly-situated police officers. Separately, another police officer, Donald Drnek, filed an individual action challenging the age limit, and the instant suit was consolidated with Drnek’s action. Although the police officers also challenged the mandatory retirement age on due process grounds, the collective bargaining agreement that the City entered into with its police officers contained a provision expressly recognizing that noth
*299
ing in that agreement precluded the City from requiring police officers to retire on or after the age of 63. R. 7 Mem. Ex. B § 10.2. In light of that provision, the district court concluded at the outset of the litigation that the police officers had no protected property interest in employment beyond the age of 63 and dismissed their due process claims.
Drnek v. City of Chicago,
. The plaintiffs asserted a companion claim for the alleged violation of their right to due process under the Illinois constitution. The court ultimately disposed of that claim on the same basis as the federal due process claim. R. 120;
Minch v. City of Chicago,
. We note that although the CBA was not attached to, and therefore not made part of, the plaintiffs’ complaint, the plaintiffs do not contest the district court's authority (or our own) to consider the CBA in evaluating the viability of their due process claim. We have recognized that when a complaint refers to and rests on a contract or other document
*301
that is not attached to the complaint, a court might be within its rights to consider that document in ruling on a Rule 12(b)(6) motion to dismiss the complaint without converting the motion into one for summary judgment, so long as the authenticity of the document is unquestioned.
Tierney v. Vahle,
. We invited supplemental briefing on the law of the case doctrine after the subject was broached by the court at oral argument.
