Under a new emergency temporary standard (ETS) from the Occupational Safety and Health Administration (OSHA), businesses with at least 100 employees must develop, implement, and enforce a policy requiring their workers to either (1) become fully vaccinated against COVID-19 or (2) undergo testing on at least a weekly basis and wear a face covering when at work. Time is short for covered employers to meet the big challenge, and here is what they need to know.