Congress enacted the Occupational Safety and Health Act in 1970. OSHA is tasked with ensuring occupational safety-that is, “safe and healthful working conditions.” It enforces occupational safety and health standards promulgated by the Secretary. Such standards must be “reasonably necessary or appropriate to provide safe or healthful employment.” They must also be developed using a rigorous process that includes notice, comment, and an opportunity for a public hearing. “Emergency temporary standards” may “take immediate effect upon publication in the Federal Register.” For such emergencies, the Secretary must show (1) “that employees are exposed to grave danger from exposure to substances or agents determined to be toxic or physically harmful or from new hazards,” and (2) that the “emergency standard is necessary to protect employees from such danger.” The emergency power has been used just nine times before. Of those nine emergency rules, six were challenged in court, and only one of those was upheld in full. On September 9, 2021, President Biden announced “a new plan to require more Americans to be vaccinated.” The Secretary of Labor, acting through the OSHA enacted a vaccine mandate which applied to roughly 84.2 million workers, covering virtually all employers with at least 100 employees. It requires that covered workers receive a Wuhan flu vaccine, and it pre-empts contrary state laws. The only exception is for workers who obtain a medical test each week at their own expense and on their own time and also wear a mask each workday. After a 2-month delay, the Secretary of Labor issued the promised emergency standard. Covered employers must “develop, implement, and enforce a mandatory vaccination policy.” The employer must verify the vaccination status of each employee and maintain proof of it. The mandate does contain an “exception” for employers that require unvaccinated workers to “undergo [weekly] testing and wear a face covering at work in lieu of vaccination.” Unvaccinated employees who do not comply with OSHA’s rules must be “removed from the workplace.” Employers who commit violations face hefty fines: up to $13,653 for a standard violation, and up to $136,532 for a willful one. OSHA has never before imposed such a mandate. Nor has Congress. Many States, businesses, and nonprofit organizations (Ps) challenged OSHA’s rule in Courts of Appeals across the country. The Fifth Circuit entered a stay. When the cases were consolidated before the Sixth Circuit, that court lifted the stay and allowed OSHA’s rule to take effect. Ps seek emergency relief arguing that OSHA’s mandate exceeds its statutory authority and is otherwise unlawful. The Supreme Court granted review.