In afternoon remarks, Biden is planning to announce that all federal employees must attest to being vaccinated against Covid-19 or face strict protocols including regular testing, masking and other mitigation measures, according to a source with direct knowledge of the matter.

The directive, which has been under review by the administration for several days, will be delivered in sterner terms than Biden has used previously, one official said.

And some states, including New York, have also said government employees must either prove they've been vaccinated or be tested weekly.

As vaccination rates have fallen across the country, Biden has become increasingly frustrated and feels as if the nation has hit "a brick wall" when it comes to getting shots in arms, according to people familiar with his thinking.

And as recently as Friday, the White House said it was the role of private-sector entities and local communities to mandate vaccines, not the federal government.

Biden's aides still say they do not believe he has the power to require all Americans to get shots.

Rochelle Walensky, director of the CDC, said Wednesday on CNN that health passes for the fully vaccinated, such as those used in parts of Europe, "may very well be a path forward."

But she acknowledged there was little the federal government could do to require vaccines in the broader population.

We are hoping that our advice will lead to more and more jurisdictions leaning in to get more people vaccinated."

A far different mindset emerges

With the Delta variant rising and new mask guidelines suddenly in place, the White House is in a far different mindset than officials had hoped at the beginning of July.

The federal government does not currently ask employees for their vaccination status, according to guidance provided to agencies by the White House-led Safer Federal Workforce Task Force.

"Federal employees and contractors may voluntarily share information about their vaccination status, but agencies should not require federal employees or contractors to disclose such information," the guidance reads.

"Responding to agency inquiries should be voluntary, and agencies should comply with any applicable laws."

White House officials have reached out to key union representatives over the last two days to lay the groundwork for Biden's decision to require federal employees to get vaccinated, according to two people familiar with the discussions.

Despite Biden's close ties to labor -- and AFL-CIO President Richard Trumka's public comments supporting vaccine mandates for workers on Tuesday -- the conversations with both public- and private-sector union officials haven't been seamless, the people said.