Petersen v. Astrue, 633 F.3d 633

WEP imposes a modified benefit formula when a beneficiary has a mix of covered and non-covered employment, to offset non-covered pension windfalls.
An exception to WEP applies when a monthly pension is based wholly on service as a member of a uniformed service, per 42 U.S.C. § 415(a)(7)(A).
Petersen worked as a National Guard technician (dual-status federal employee) from 1972 to 2000 and began civil pensions in 2000.
Petersen’s pension payments were based on his service in the National Guard, which required uniform wear, military drills, and Guard membership.
SSA initially applied WEP to Petersen’s old-age benefits; ALJ reversed, finding the uniformed-service exception applied; Appeals Council reversed again.
District court held Petersen’s pension was based wholly on uniformed-service service, triggering the exception and reversing SSA, which SSA challenged on appeal.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether WEP exception applies when pension is based wholly on uniformed service	Petersen	Astrue	Yes; pension based wholly on uniformed-service service.
Whether National Guard technician status affects “as a member of the uniformed services” wording	Petersen	Astrue	Plain language supports exception; dual-status does not defeat it.
Whether the district court's interpretation should be deferred to SSA	Petersen	Astrue	No deferential deference; statute unambiguous; no need to defer.

Jimenez v. Quarterman, 555 U.S. 113 (2009) (plain-language statutory interpretation controls when unambiguous)
United States v. McAllister, 225 F.3d 982 (8th Cir.2000) (clear statutory language ends inquiry)
Reutter ex rel. Reutter v. Barnhart, 372 F.3d 946 (8th Cir.2004) (deference to agency interpretations recognized but not compelled when statute clear)
Smith v. Sullivan, 982 F.2d 308 (8th Cir.1992) (appropriate deference when agency fills statutory gap)
TeamBank, N.A. v. McClure, 279 F.3d 614 (8th Cir.2002) (gap-filling deference under Chevron framework)