WASHINGTON - U.S. President Joe Biden is expected to announce on Thursday that all civilian federal workers will need to be vaccinated against the coronavirus or face regular testing, social distancing, mask requirements and travel limits, a source familiar with the matter said.

Biden, who will deliver remarks on COVID-19 at the White House at 4 p.m. (2000 GMT) on Thursday, will not mandate vaccines for federal employees and those who decide against getting a vaccine will not be at risk of being fired, the source said.

The United States has about 2.18 million civilian employees and another 570,000 people work for the U.S. Postal Service (USPS), according to 2020 data. It is not clear if Biden plans to apply the requirement to the postal service or to contractors who work for the federal government.

CNN first reported Biden's plan late on Tuesday.

Some states and New York City have announced similar requirements, said the source, who declined to be identified.

For example, New York Governor Andrew Cuomo said on Wednesday that state employees will be required to be vaccinated or get tested weekly.

The U.S. Department of Veterans Affairs on Monday mandated that its doctors and other medical staff get COVID-19 vaccines, becoming the first federal agency to impose such a requirement.

The VA comprises the largest U.S. healthcare system, employing more than 367,200 full-time healthcare professionals and support staff at 1,293 facilities, according to its website.

On Tuesday, Biden said his administration was considering the requirement for federal employees. 

Numerous U.S. agencies on Wednesday mandated masks at federal buildings in COVID-19 hot spots in line with instructions issued by the White House Office of Management and Budget (OMB), according to an OMB email seen by Reuters. 

The Defense Department said late Wednesday that the masking requirements would apply to the Pentagon.

The White House also said masks are required indoors in federal buildings for all employees and visitors, whether or not they are vaccinated, in those areas experiencing sharp increases in infections.

On Wednesday, the Centers for Disease Control and Prevention (CDC) said nearly 67% of U.S. counties were at substantial or high transmission rates, up from 63.4% on Tuesday.

The federal government is racing to contain the pandemic in the hope of avoiding nationwide shutdowns, as the virulent Delta variant of the coronavirus blazes through parts of the United States and immunizations lag.

AFL-CIO President Richard Trumka told C-SPAN that the union supports vaccine mandates.

"If you come back in and you are not vaccinated, everybody in that workplace is jeopardized," Trumka said Tuesday.

The American Postal Workers Union (APWU) said it opposes a vaccine mandate for federal employees and expressed concern about Biden's expected announcement.

"While the APWU leadership continues to encourage postal workers to voluntarily get vaccinated, it is not the role of the federal government to mandate vaccinations for the employees we represent," the group said in a statement.

(Reporting by David Shepardson and Nandita Bose in Washington; editing by Grant McCool, Robert Birsel) ((nandita.bose@thomsonreuters.com; +12023545868; Reuters Messaging: nandita.bose.reuters.com@reuters.net))