On Thursday, senior Biden administration officials announced details of a highly anticipated mandate requiring U.S. employers with 100 or more workers to ensure employees are either fully vaccinated for COVID-19 or tested each week for the virus.

The officials also unveiled details of a separate mandate that will require employers participating in Medicare or Medicaid to have a fully vaccinated workforce, with no testing alternative.

The first rule covers 84 million U.S. workers, or two-thirds of the U.S. workforce, officials said. That rule, which will be administered by the Labor Department’s Occupational Safety and Health Administration, will require employees to be fully vaccinated by Jan. 4.

Employees who aren’t fully vaccinated by Jan. 4 have to produce a verified negative test to their employers every week and begin wearing a mask at work as of Dec. 5. Workers who test positive for COVID-19 or receive a diagnosis from a licensed health care provider have to be removed from the workplace. The rule doesn’t require employers to pay for the tests, though agreements with unions might require employers to cover the bill.

Starting Dec. 5, the OSHA rule will require covered employers to provide workers with paid time time off to receive vaccinations, as well as sick leave to recover from vaccination side effects that preclude working.