The US Postal Service has suspended new policies that were decried as an attempt to sabotage the 2020 election.
Postmaster General Louis DeJoy said on Tuesday he would reverse operations changes that critics say would hamper mail-in voting.
The u-turn comes as Mr DeJoy is due to testify to Congress and at least 20 states were preparing to sue.
There is a fierce debate over postal funding in 2020, as record numbers of Americans are expected to vote by mail.
The US Postal Service (USPS) under Mr DeJoy had begun what it said were cost-cutting measures in recent months.
However, in a sharp reversal, Mr DeJoy has now said that post office hours would not be cut and no further post boxes or sorting machines would be removed.
Mr DeJoy, a former Republican donor, also said overtime pay would continue to be approved to ensure deliveries arrive on time.
“To avoid even the appearance of any impact on election mail, I am suspending these initiatives until after the election is concluded,” Mr DeJoy said in a statement.
The development comes as the row over the politicisation of the most popular US government agency has become the top issue in the 2020 presidential campaign. Over the weekend, former President Barack Obama – in what was regarded as his most high profile criticism of his successor to date – accused Mr Trump of trying to “actively kneecap” the postal service.
Nancy Pelosi, the Speaker of the House, quickly cheered the postmaster’s decision, telling reporters: “They felt the heat and that’s what we were trying to do, make it too hot to handle.” On Sunday, Ms Pelosi had recalled the House from a recess in order to investigate the USPS policies.
Mr DeJoy, a major political donor who was appointed by Mr Trump to lead the USPS in May, is due to testify to a Republican-led Senate committee on Friday, and then to a Democrat-led House committee on Monday.
Last week, President Trump said he rejected a funding boost for the USPS to shore up a predicted influx mail-in voting, claiming without evidence that it would lead to voter fraud and help Democrats.
Voting by mail is not new to the US. According to Reuters, approximately one in every four voters cast ballots by mail in 2016.