President Joe Biden’s latest vaccination push is the most aggressive effort yet by his administration to get the raging coronavirus pandemic under control.

Critics see the move by the president as a reversal of his previous promise to avoid vaccine mandates. Federal health officials, however, believe it is the next step in the fight against the highly contagious delta variant, which is killing more than 1,500 Americans every day, according to a CNBC analysis of Johns Hopkins University data, and filling hospitals in unvaccinated pockets of the country to the brim.

“We’re going to protect vaccinated workers from unvaccinated coworkers,” Biden said Thursday in announcing the plan. “We’re going to reduce the spread of Covid-19 by increasing the share of the workforce that is vaccinated in businesses all across America.”

The multipronged approach affects hundreds of public and private companies and tens of millions of American workers. It mandates vaccines and eliminates testing options for federal government employees, including those in the health-care sector, and calls for stiff penalties for those who don’t comply.

Here’s what you need to know about Biden’s latest bid to get more Americans vaccinated.

Where vaccination is mandatory, with no testing option

Federal employees and contractors that work with the government face renewed vaccine mandates and will no longer have the option of regular Covid testing.

“If you want to work with the federal government and do business with us, get vaccinated,” Biden said. “If you want to do business with the federal government, vaccinate your workforce.”

Health-care workers also face strict mandates. The president has ordered all health-care facilities that receive federal Medicaid or Medicare funding to mandate vaccines for their workforces with no testing option.

Previously, the Biden administration mandated vaccines only for employees at U.S. nursing homes receiving federal funding. Some states, including New York and Maine, had already mandated vaccines for health-care workers.

The new rules will affect more than 17 million health workers at more than 50,000 hospitals and health-care facilities across the U.S.

“If you’re seeking care at a health-care facility, you should be able to know that the people treating you are vaccinated,” Biden said. “Simple, straightforward, period.”

The president also ordered all staff at Head Start programs run by the federal government to be vaccinated. The order extends to schools run by the Bureau of Indian Affairs and the Department of Defense, affecting about 300,000 people in total, according to Chalkbeat, a news organization that covers education.

Where vaccination or weekly testing is mandatory

Despite the broad scope of the president’s push, most U.S. workers, more than 80 million, will still have the option of proving they are not carrying the virus by submitting to weekly Covid tests.

To boost the pace of daily shots, which have slowed down after a spike in mid-August, the president ordered the Department of Labor to create a new rule requiring any company with more than 100 employees to mandate vaccines for their employees or weekly Covid tests for workers who cite religious or health reasons for not getting vaccinated. However, those reasons for opting out are likely to be more scrutinized by employers going forward.

The new rule will be implemented by the Labor Department’s Occupational Safety and Health Administration, or OSHA. OSHA can issue an emergency temporary standard if it proves that employees are in danger and that the proposed rule can avert that danger.

Employers will also be ordered to provide paid time off for employees to get vaccinated. This applies to both the public and private sectors.

“No one should lose pay in order to get vaccinated or take a loved one to get vaccinated,” Biden said.

Consequences for violating the rules

Most Americans support vaccine mandates in workplaces, with 62% of Americans backing the idea, according to an August poll by USA Today and Ipsos.

Still, among the 29% of U.S. voters who are unvaccinated, 83% say they do not plan to get the lifesaving shots, a new CNBC survey shows.

Employees who fail to comply with the new mandates could face a range of consequences, including termination, as companies feel pressure to fall in line.

Companies will face a $13,600 penalty per violation of the OSHA rule, though the new rules could take some time to implement and enforce. OSHA has experienced a steady decline in staffing and currently provides one inspector for every 83,000 workers, according to the AFL-CIO, the largest federation of unions in the U.S.

Appeal to unvaccinated Americans

In his announcement, Biden questioned why 80 million Americans have still not received the shots after they were made free and accessible and were approved by the Food and Drug Administration.

“What more is there to wait for? What more is there to see?” Biden said. “We’ve been patient, but our patience is wearing thin.”

Biden appealed to those running large entertainment venues, sports arenas and movie theaters to require vaccination or proof of a negative test for entry. New York City and San Francisco already require proof of vaccination for activities such as dining indoors and attending movies and entertainment venues, with New York City requiring proof of at least one dose and San Francisco requiring proof of full vaccination.

Biden also asked physicians across the country to “reach out to unvaccinated patients … and make a personal appeal to them to get the shot.”

About 75% of U.S. adults have received at least one dose of a Covid vaccine and about 54% of all Americans are fully vaccinated, according to Centers for Disease Control and Prevention data. Experts are still split on what percentage of a population needs to be vaccinated in order for the population to reach herd immunity, though estimates range between 70% and 90%.

“This is not about freedom or personal choice. It’s about protecting yourself and those around you,” Biden said.