It’s the government’s most aggressive—and most controversial—action in its battle against COVID-19 to date. Many GOP governors have voiced opposition to the plan and court battles are already underway. A suit filed in U.S. District Court in Washington on Sept. 23 aims for an injunction to halt required vaccinations for federal workers and troops.

The situation is changing regularly, but here’s what we know right now.

When does the vaccine mandate go into effect?

That’s still not clear. The Department of Labor’s Occupational Safety and Health Administration (OSHA) has not yet issued the “emergency temporary standard” (ETS) that will put the mandate into effect. And that issuance will include a ramp-up period. There are also the aforementioned legal battles, which could slow things down or prevent the mandate from being issued altogether.

At this point, the best guess is, barring a court injunction, the ETS will be issued before the end of October, though enforcement won’t begin for 75 days or so.

How many private businesses will be impacted by the vaccine mandate?

Not as many as it might seem. The mandate applies to private employers with more than 100 employees, which is largely major corporations. The North American Industry Classification System only counts 170,580 businesses in that range. (Though the group notes it does not have employee counts for 1.77 million companies.)

The 100-worker figure will be counted on a company-wide basis, not per office.

How many workers will be affected by the vaccine mandate?

That’s a bigger number. The White House estimates the mandate will impact 80 million workers in the private sector. Another 17 million workers at nursing home facilities and hospitals that receive Medicare and Medicaid funds, along with the staff of federal Head Start and Early Head Start programs, will also be affected.

All totaled, roughly two-thirds of the U.S. workforce will be covered by the mandate.

If I don’t want to get the vaccine, what are my options?

Workers who refuse to get vaccinated will have to pass a weekly COVID-19 test to come to work.

Will remote workers have to be vaccinated?

No. The Labor Department said on Sept. 10 that remote workers who do not come into contact with others will not be impacted by the mandate. That changes if they come into the workspace, however.

Will the vaccine mandate affect my union agreement?

It shouldn’t. The Labor Department said the ETS, like other OSHA standards, will not change any collective bargaining agreement standards.

Which businesses aren’t covered by the vaccine mandate?

Small businesses with less than 100 employees are not affected by the federal mandate (though they could, of course, impose company mandates on their own).

What else is impacted by the vaccine mandate?

Biden’s vaccine mandate goes beyond the workplace. Under his proposal, vaccination is mandatory to attend events in sports arenas, large concert halls, and other venues that attract large groups of people. Outdoor football stadiums were not mentioned, though.

Who will enforce the vaccine mandate?

OSHA is ultimately in charge of enforcement. There is no system in place to track or report vaccination status, however, so any enforcement will likely come from employee complaints. (They’ll be legally protected from retaliation by their employers, though that’s not a foolproof system.)

What are the punishments for businesses that don’t comply with the vaccine mandate?

Companies that refused to go along with the mandate could face fines of up to $13,653—which is the maximum amount OSHA can penalize a business.

Who pays for the vaccine mandate’s testing?

Good question—and one that doesn’t yet have an answer. Law firm Fisher Phillips notes that typically “any testing protocols must comply with applicable wage and hour laws, which provide that time spent on receiving employer-required tests should almost always be treated as compensable.”

The final answer will be included in OSHA’s ETS when it is released.

How long will the mandate last?

OSHA’s ETS can last up to six months. If the Biden administration hopes to extend the vaccine mandate beyond that, OSHA will have to make it a permanent standard, which makes it subject to a comment period and more formal rules.

What does the vaccine mandate mean for federal workers?

Federal workers and contractors already have to be vaccinated or take regular COVID tests. With the mandate, the testing option is removed—and they’ve got 75 days from Biden’s announcement to receive their jab. Those that don’t—and don’t have a legitimate religious or medical exemption—could face warnings, suspensions, or could be fired.

Service members and Department of Defense employees fall under the mandate’s orders, as do the National Institutes of Health and Department of Veteran Affairs.

Not every federal worker is covered though. The mandate does not apply to non-executive branch employees such as members of Congress or judicial employees, for instance.