(Bloomberg) -- President Joe Biden will require federal workers to prove they’ve been vaccinated against Covid-19 or wear masks and submit to frequent coronavirus testing as the highly contagious delta variant is causing cases to spike in the U.S.

The rules will cover millions of federal workers, including the military and on-site contractors, according to the White House. Biden, who will announce the requirement Thursday, also asked his team to take steps to apply similar standards to all federal contractors and encourage private sector employers to follow the same approach.

The requirements come in response to vaccine holdouts, whose refusal to get shots has allowed the delta variant to spread.

Biden’s administration had hoped that most Americans would voluntarily choose to be vaccinated, limiting the ability of the virus to spread. But only about 49% of the U.S. population is fully vaccinated. In recent days, there’s been a rebound in first shots in a few of the worst-hit states.

In the spring, Biden set the goal of at least partially vaccinating 70% of American adults by July 4, which the country failed to meet. At the same time, the delta variant took root across the country, largely infecting the unvaccinated but also spreading to inoculated people.

But with cases rising and companies and municipalities beginning to require their employees be vaccinated, Biden is taking the same step for federal workers. The federal government employs more than 4 million people, including more than 2 million in the civilian workforce.

The virus surge poses a serious political threat to the president, who promised a “summer of joy” on July 4 as he declared America’s independence from Covid-19. Biden had counted on plummeting case rates to anchor the economic recovery and his policy agenda.

Also Thursday, Biden will announce that small- and medium-size businesses will be reimbused for offering employees paid leave to get family members vaccinated, according to the White House. The president also will call on states and localities to incentivize vaccinations, including offering $100 to get shots.

Biden plans to call on school districts nationwide to host at least one vaccination clinic in coming weeks to administer shots to kids 12 and over, the group that’s eligible to receive them.

Biden is also directing the Defense Department to determine how and when to add Covid-19 vaccinations to other shots required for members of the military, according to the White House.

On Tuesday, the Centers for Disease Control and Prevention tightened its guidance, advising Americans to wear masks in public indoor places located in areas with substantial spread. With the District of Columbia’s case rate hitting the threshold set out by the CDC, the White House began requiring staff and journalists to cover their noses and mouths while inside the buildings on its grounds.

The policy for federal workers also follows the Department of Veterans Affairs’ Monday announcement that it will require all of the agency’s front-line health care workers to be vaccinated.

The U.S. recorded more than 80,000 new cases on Tuesday, driving the rolling seven-day average to more than 61,000, according to the CDC. The rolling average case rate is about five times higher than it was a month ago, before the delta variant became the dominant U.S. strain.

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