The U.S. Supreme Court's recent decision invalidating the Occupational Safety and Health Administration's (OSHA) vax-or-test mandate for certain businesses is the latest in a growing number of challenges to federal, state, and municipal workplace vaccination requirements. These suits have caused considerable confusion for employers, employees, and, where applicable, their unions. The varied dispositions—with most mandates upheld—often hinge on an agency's enabling statute and the specific aspect of a mandate challenged.