“Americans should not have to choose between their health and their vote,” she added.
Later on Sunday, top Senate Democrat Chuck Schumer also called on the Republican-led Senate to reconvene early to vote on the House’s bill.
The U.S. Congress was not due to resume until Sept. 8.
House speaker Pelosi’s letter comes as mail-in voting has become a point of contention in the run-up to the November vote and after Democrats in Congress already called on the heads of the postal service to testify at an urgent hearing on Aug. 24.
Earlier on Sunday, Democratic leaders requested Postmaster General Louis DeJoy and Chairman of the USPS Board of Governors, Robert Duncan to appear before the U.S. House of Representatives.
The coronavirus pandemic has forced many Americans to stay home and Democrats have asked for 25 billion dollars in additional funding for the postal service to ensure people can vote from home using mail-in ballots.
U.S. President Donald Trump, however, has argued that mail-in ballots are vulnerable to voter fraud.
There is no evidence to support the idea that either absentee or mail-in ballots contribute to voter fraud.
Meanwhile, congressional Democrats allege that organisational changes at the postal service are “slowing the mail and jeopardising the integrity of the election,” while criticising Trump’s efforts to block emergency funding.
“The President has explicitly stated his intention to manipulate the Postal Service to deny eligible voters access to the ballot in pursuit of his own re-election,” read an earlier statement from Pelosi and Schumer, among others.
“Alarmingly, the Postmaster General – 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 and delay the mail,” the statement continued.
Senate Democrats started an official investigation last week into delays in mail delivery. (dpa/NAN)