The Industrial Union Department, AFL-CIO v. American Petroleum Institute et al., 1979 is a landmark US Supreme Court case that dealt with the Occupational Safety and Health Administration's (OSHA) authority to regulate workplace safety. The court ruled in favor of the American Petroleum Institute, stating that OSHA had exceeded its mandate by setting limits on benzene exposure without proving it posed a significant risk at low levels. This decision established an important precedent for future regulatory cases: agencies must demonstrate substantial evidence of potential harm before they can impose regulations or restrictions on businesses. It also underscored the necessity for cost-benefit analysis in determining whether such regulation is warranted.

In the dissenting opinion for Industrial Union Department, AFL-CIO v. American Petroleum Institute et al., Justice Marshall argued that the majority's decision was a departure from Congress' intent when it enacted the Occupational Safety and Health Act (OSHA). He believed that OSHA was designed to give broad authority to the Secretary of Labor to set safety standards in workplaces based on best available evidence and technology, not just proven significant risks. The majority's requirement for definitive proof of harm before setting any standard would make it almost impossible for OSHA to fulfill its mandate. Furthermore, he disagreed with their interpretation of "feasibility," arguing that economic considerations should be secondary when worker health is at stake. Lastly, he criticized their dismissal of benzene as non-threatening despite substantial evidence suggesting otherwise.