The announcement will come in remarks where Biden is also expected to lay out a series of new steps, including incentives, in an attempt to spur new vaccinations as the Delta variant spreads rapidly throughout the country. It will also follow the decision by the Department of Veterans Affairs to require its frontline health care workers to be vaccinated over the course of the next two months.

Biden alluded to the looming announcement on Tuesday.

"That's under consideration right now," Biden said, when asked if he would impose a vaccination mandate on federal workers.

While the specifics are still being finalized, the source said, federal workers would be required to attest to their vaccination status or submit to regular testing. The source said the proposal will be roughly similar to what is being implemented in New York City. Additional requirements for the unvaccinated could be added as agencies push to vaccinate their employees.