The Democratic-led US House of Representatives has voted to provide the nation’s cash-strapped postal service with $US25 billion ($35 billion) and block policy changes that have stirred concerns about mail-in voting before the November 3 presidential election.

The 257-150 vote sent the legislation, dubbed the delivering for America act, on to the Republican-controlled Senate.

Senate Majority Leader Mitch McConnell said in a statement it would “absolutely not pass” the stand-alone bill.

The White House also strongly opposes the legislation and has said it will recommend US President Donald Trump veto the measure.

But more than two-dozen House Republicans broke ranks to join Democrats in approving the bill during a rare Saturday session called by House Speaker Nancy Pelosi in the middle of the congressional August recess.

With postal voting expected to surge during the coronavirus pandemic, Mr Trump has alarmed Democrats by repeatedly denouncing mail-in ballots as a possible source of fraud.

Louis DeJoy has been a controversial appointee as postmaster-general. Photo: AP

Postmaster-general Louis DeJoy recently suspended cost-cutting measures that slowed deliveries in recent weeks.

Democrats, who accuse Mr Trump of trying to discourage postal voting to gain an electoral advantage over Democratic presidential nominee Joe Biden, have cast themselves as defenders of a public that relies on the United States Postal Service for vital deliveries, including prescription drugs.

“The American people do not want anyone messing with the post office,” Democratic Representative Carolyn Maloney, who authored the legislation, said.

“They certainly do not want it to be politicised.

“They just want their mail, they want their medicines and they want their mail-in ballots delivered in a timely way. And that is exactly what our bill does.”

So now the Democrats are using Mail Drop Boxes, which are a voter security disaster. Among other things, they make it possible for a person to vote multiple times. Also, who controls them, are they placed in Republican or Democrat areas? They are not Covid sanitized. A big fraud!

— Donald J. Trump (@realDonaldTrump) August 23, 2020

Ms Maloney also released a USPS document showing an 8 per cent slowdown in the processing of first-class mail, most of it occurring after Mr DeJoy became postmaster in June.

As representatives prepared to vote, Mr Trump took to Twitter to accuse Ms Pelosi and Senate Democratic leader Chuck Schumer of seeking unnecessary funding for the USPS and trying to pull off a “universal mail-in ballot scam”.

“Vote NO to the Pelosi/Schumer money wasting HOAX which is taking place now,” Mr Trump wrote.

Mr DeJoy’s downsizing drive has included curbs on overtime and removal of post boxes.

The USPS’s inspector-general said earlier this month the cost-cutting measures would be investigated – along with potential conflicts of interest related to Mr DeJoy’s ownership of millions of dollars in stock in USPS’s rivals and customers, according to a financial disclosure form filed by his wife.

-Reuters