Speaker Nancy Pelosi on Sunday said she would recall the House of Representatives from its summer recess to vote this week on an act "to save the Postal Service".
Pelosi and fellow senior Democrat Chuck Schumer also called for Postmaster General Louis DeJoy, a recent Trump appointee, to appear before an "urgent hearing" of the House oversight committee.
They said that DeJoy — "a Trump mega-donor — has acted as an accomplice in the president’s campaign to cheat in the election, as he launches sweeping new operational changes that degrade delivery standards."
"This is a crisis for American democracy," progressive senator Bernie Sanders said on ABC's "This Week".
Democrats expect to use the issue to mobilize voters when the party opens its national convention on Monday — in a virtual format — with former vice president Joe Biden slated to accept the party's nomination on Thursday. Republicans follow a week later.
Trump's chief of staff, Mark Meadows, said the Democrats could yet obtain more postal funding if they are ready to make a deal on the stimulus package.
"If my Democrat friends are all upset about this, come back to Washington," he told CNN's "State of the Union".
"Put the postal funding in there" along with aid to small businesses, he said. "We'll pass it tomorrow."