Tens of millions of Americans who work at companies with 100 or more employees will need to be vaccinated against COVID-19 by Jan. 4 or get tested for the virus weekly. The new government rules were issued Thursday.

The Occupational Safety and Health Administration (OSHA) says companies that fail to comply could face penalties of nearly $14,000 per violation.

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The new requirements were first previewed by President Joe Biden in September. They will apply to about 84 million workers at medium and large businesses.

It is not clear how many of those employees are unvaccinated.

A senior administration official says the agency would target companies if it gets complaints.

Answers to 25 common COVID-19 vaccine questions

Vaccinations for COVID-19 began being administered in the U.S. on Dec. 14, 2020. The quick rollout came a little more than a year after the virus was first identified in November 2019. The impressive speed with which vaccines were developed has also left a lot of people with a lot of questions. The questions range from the practical—how will I get vaccinated?—to the scientific—how do these vaccines even work?

Keep reading to discover answers to 25 common COVID-19 vaccine questions.