WASHINGTON – President Joe Biden is expected to announce Thursday evening a new requirement for federal employees to receive the coronavirus vaccine, a source familiar with the matter told NBC News.

The executive order will also extend to contractors that work with the U.S. government, impacting a total of 2.1 million employees.

The person, who spoke on the condition of anonymity, said the decision will be announced during the president’s address at 5 p.m. EST.

Earlier this year, Biden ordered all federal employees to prove their coronavirus vaccination status or submit to a series of rigorous safety protocols. Thursday’s order will remove the option for rigorous testing, the person said, as the United States struggles to contain the highly contagious delta variant.

Biden’s decision comes as his administration searches for ways to make inroads against the mutating virus. His campaign to bring the pandemic under control by summer has largely failed in the face of resistance to vaccination among a significant segment of the U.S. population. Infections and deaths are spiking among people who haven’t been immunized.

The U.S. is currently averaging more than 151,000 new Covid cases a day, far above the 36,000 cases at this time last year before vaccines were available, according to a CNBC analysis of data from Johns Hopkins University. Nearly 1,500 people are dying a day on average from Covid.

In total, 62% of the U.S. population has received at least one dose of a vaccine – Pfizer, Moderna or Johnson & Johnson – while 53% are fully vaccinated.

“This is an American tragedy. People are dying, and will die, who don’t have to die,” Biden said during a White House address in July.

“This is not about red states and blue states. It’s literally about life and death,” he said. “With freedom comes responsibility. Your decision to be unvaccinated impacts someone else.”

A more comprehensive federal mandate could influence state governments to follow suit, according Jen Kates, director of global health and HIV policy at the Kaiser Family Foundation. Currently, some 20 states have some kind of vaccine mandate in place for government or health-care workers, though many have opt outs for people who want to submit to regular testing instead.

In July, the Department of Veterans Affairs announced it would order its health-care workers to get inoculated, making it the first federal agency to impose such a mandate. Veteran Affairs Secretary Denis McDonough described the new measure as “the best way to keep Veterans safe.”

A month later, the Food and Drug Administration fully approved Pfizer and BioNTech’s Covid-19 vaccine, the first in the U.S. to win the coveted designation. The mRNA vaccine, which will be marketed as Comirnaty, was on the U.S. market under an Emergency Use Authorization that was granted by the FDA in December.

The FDA’s approval was expected to give even more businesses, schools and universities across the country greater confidence to adopt vaccine mandates.

More than 214 million doses of the Pfizer vaccine have been administered, according to data compiled by the Centers for Disease Control and Prevention. Approximately 96 million people in the U.S. are fully vaccinated with Pfizer’s two-dose vaccine.

Following the FDA’s approval of Pfizer, the Pentagon updated its health guidance to require all U.S. service members and defense contractors to receive the coronavirus vaccine.

The Moderna and Johnson & Johnson vaccines are still administered under emergency use authorizations.

CNBC’s Kevin Breuninger contributed to this report from New York.