The Biden administration yesterday set Jan. 4 as the deadline for large companies to mandate coronavirus vaccinations or start weekly testing for their workers. The rule is expected to cover 84 million workers, roughly 31 million of whom are unvaccinated.

It is the most far-reaching and potentially controversial measure in the government’s efforts to fight the pandemic. “While I would have much preferred that requirements not become necessary, too many people remain unvaccinated for us to get out of this pandemic for good,” President Biden said.

How will it work in practice? Many questions remain, on everything from enforcement to exemptions. Go here for answers to frequently asked questions about what the mandate means for companies and workers. You can also submit more questions for us to consider — we’ve been updating the article frequently. Here are the high-level details:

The timing. Setting an early January deadline gives retailers and logistics companies, which are strapped for employees, time to get through the holiday shopping season before instituting the requirements. But the National Retail Federation was still sharply critical of the move. “The Biden administration has chosen to declare an ‘emergency’ and impose burdensome new requirements on retailers during the crucial holiday shopping season,” it said.

The requirements. Workers are considered fully vaccinated if they have received two doses of the Pfizer-BioNTech or Moderna…

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