The move followed guidance issued by the Centers for Disease Control and Prevention (CDC) on Tuesday that vaccinated people should wear masks indoors in areas with substantial or high COVID-19 community transmission.
The White House said masks are required indoors in federal buildings for all employees and visitors, whether or not vaccinated, in those areas.
On Wednesday, CDC said nearly 67% of U.S. counties were at those 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 future nationwide shutdowns, as the virulent Delta variant of the coronavirus blazes through parts of the United States and immunizations lag.
President Joe Biden is expected to announce further mandates for federal agencies on Thursday. read more In an email sent to all federal agencies late on Tuesday, Jason Miller, OMB's deputy director for management, said in line with the CDC guidance, "in areas of substantial or high community transmission, agencies must require all federal employees, onsite contractors, and visitors, regardless of vaccination status, to wear a mask inside of federal buildings. As of today, that includes the Washington, D.C., area."
It added that people "not fully vaccinated also need to continue to physically distance consistent with CDC guidance."
The Pentagon said it was immediately requiring indoor masking at all Defense Department properties in areas with substantial or high transmission rates.
Biden's administration on Monday required that all Veterans Affairs staff receive vaccinations, and on Wednesday, the Department of Homeland Security said in a Twitter post all of its 240,000 employees, will need to wear a mask indoors and physically distance, effective immediately and regardless of vaccination status.
Biden first issued an executive order in January mandating all people wear masks in federal buildings but the policy was relaxed in May when the CDC said fully vaccinated Americans did not need to wear masks in most indoor settings.
The Energy and Interior Departments also said they had implemented the policy.
The White House and the U.S. House of Representatives both said they were requiring vaccinated people to wear masks indoors in government buildings.