Mayo Foundation for Medical Education & Research v. United States, 131 S. Ct. 704

Mayo Foundation and Mayo Clinic offer medical residency programs with hands-on patient care and a formal educational component; residents are paid stipends and receive benefits.
FICA taxes apply to wages; the statute exempts services of a student employed by a school if the student is enrolled and regularly attending classes.
In 2004 the Treasury adopted a full-time employee rule limiting the student exemption for workers 40 hours or more per week, stating such services are not incident to pursuing a course of study.
Mayo challenged the rule as inconsistent with the statute; district court sided with Mayo, but the Eighth Circuit reversed, applying Chevron deference to the regulation.
The Supreme Court granted certiorari to determine the correct framework and whether the rule is a reasonable interpretation of §3121(b)(10).
The Court held that the full-time employee rule is a reasonable construction of §3121(b)(10) and affirmed the Eighth Circuit.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether Congress directly addressed residents as students under §3121(b)(10).	Mayo argues residents fit the student exemption under a broad dictionary reading.	US contends Congress did not define student to include residents under the exemption.	Congress has not addressed the question.
What framework governs review of an ambiguous tax provision: Chevron step two or National Muffler factors.	Mayo seeks National Muffler multi-factor review.	US argues Chevron deferential step-two review applies.	Chevron framework governs review; uniform approach upheld.
Is the full-time employee rule a reasonable interpretation of §3121(b)(10)?	Mayo contends case-by-case inquiry should determine student status.	US defends rule distinguishing education from service by hours worked to improve administrability.	Yes; the rule is a reasonable construction.
Does the Department’s rule deserve Chevron deference given notice-and-comment procedure and delegation?			The rule falls within Chevron deference due to explicit delegation and notice-and-comment.

Chevron U.S.A. Inc. v. Nat. Resources Def. Council, Inc., 467 U.S. 837 (1984) (establishes Chevron deference framework for agency interpretations)
National Muffler Dealers Ass'n., Inc. v. United States, 440 U.S. 472 (1979) (multifactor approach to evaluating agency regulations when ambiguity exists)
United States v. Mead Corp., 533 U.S. 218 (2001) (clarifies when Chevron deference applies to agency interpretations of statutes)
Rowan Cos. v. United States, 452 U.S. 247 (1981) (less deference for general authority; pre-Chevron context)
Long Island Care at Home, Ltd. v. Coke, 551 U.S. 158 (2007) (factors for evaluating agency rulemaking under Chevron/Mead framework)
Smiley v. Citibank (South Dakota), N.A., 517 U.S. 735 (1996) (no externalities negate validity of regulations; context for interpretive authority)
Vogel Fertilizer Co. v. United States, 455 U.S. 16 (1982) (precedent on deference to agency interpretations under general authority)