Yellow Freight System (plaintiff), an interstate trucking company, hired Thomas E. Moyer (defendant) as a truck driver. On February 29, 1988, Moyer’s truck broke down. Yellow Freight instructed Moyer to find a nearby telephone, contact a Yellow Freight mechanic, and return to his truck. However, upon exiting the truck, Moyer aggravated an old medical injury and went to the hospital. Yellow Freight suspended Moyer for failing to follow company procedures after the truck broke down. Between June and October 1988, Yellow Freight issued four warning letters to Moyer for being unavailable for work. Yellow Freight issued the fourth letter after Moyer testified on behalf of a fellow employee at a grievance hearing. On November 9, 1988, Yellow Freight terminated Moyer’s employment. Moyer filed a complaint with the Secretary of Labor alleging Yellow Freight violated § 405(b) of the Surface Transportation Assistance Act when it discharged him in retaliation for his refusal to drive after his injury. The Department of Labor’s Occupational Safety and Health Administration (OSHA) advised Yellow Freight of the alleged violation of § 405(b) and later found no violation occurred. Moyer objected to OSHA’s finding and requested an administrative hearing. At the hearing, Moyer testified that he might have been discharged in response to his testimony at his fellow employee’s grievance hearing in violation of § 405(a) of the Act. Yellow Freight only defended against the § 405(b) allegation at the hearing. The administrative law judge found Yellow Freight did not violate § 405(b) and determined there was insufficient evidence to find a violation of § 405(a). The Secretary reviewed the record and concluded that although Yellow Freight did not violate § 405(b), it violated § 405(a). Yellow Freight petitioned the Court of Appeals to review the Secretary’s decision.