In the case of Oscar Mayer & Co. et al. v. Evans, 1978, the Supreme Court was tasked with deciding whether a state agency's decision on an age discrimination claim precluded federal court action under the Age Discrimination in Employment Act (ADEA). The plaintiff, Evans had filed his complaint with both Iowa Civil Rights Commission and Equal Employment Opportunity Commission (EEOC), but only received a right-to-sue letter from EEOC after filing suit in Federal District Court which dismissed his claim due to procedural reasons. The Supreme Court held that dismissal was incorrect as ADEA requires complainants to initiate proceedings with relevant state agencies before moving onto federal courts; however it does not require termination of these proceedings before initiating federal action. Furthermore, they clarified that while exhaustion of remedies is required for Title VII claims (gender/race/religion/national origin discrimination), this requirement doesn't apply for age-based complaints under ADEA because its language differs significantly from Title VII’s provisions.

In the dissenting opinion for Oscar Mayer & Co. v. Evans, Justice Rehnquist disagreed with the majority's interpretation of procedural requirements under the Age Discrimination in Employment Act (ADEA). He argued that Congress intended to create a uniform federal system for handling age discrimination complaints, not one where state procedures could supersede or complicate federal ones. The majority's decision would lead to unnecessary confusion and inconsistency because it required claimants in some states but not others to first pursue their claims at the state level before filing a federal lawsuit. This discrepancy was due to variations among states' own anti-discrimination laws and enforcement mechanisms which were inconsistent with ADEA’s purpose of creating a unified national approach against age discrimination.