WASHINGTON (AP) — Speaker Nancy Pelosi is calling the House back into session over the crisis at the U.S. Postal Service, setting up a political showdown amid growing concerns that the Trump White House is trying to undermine the agency ahead of the election.

Pelosi is cutting short lawmakers' summer recess with a vote expected Saturday on legislation that would prohibit changes at the agency as tensions mount. President Donald Trump's new postmaster general, Louis DeJoy, has sparked nationwide outcry over delays, new prices and cutbacks just as millions of Americans will be trying to vote by mail to avoid polling places during the coronavirus outbreak.

Trump on Monday defended the agency's embattled new leader, a major Republican donor, but also criticized postal operations and claimed that universal mail-in ballots would be "a disaster."

"I want to make the post office great again," Trump said on "Fox & Friends." Later at the White House he denied asking for a mail-delivery slow down.

The decision to recall the House, made after a weekend of high-level leadership discussions, carries a political punch. Voting in the House will highlight the issue after the weeklong Democratic National Convention nominating Joe Biden as the party's presidential pick and pressure the Republican-held Senate to respond. Senate Majority Leader Mitch McConnell sent senators home for a summer recess.

"In a time of a pandemic, the Postal Service is Election Central," Pelosi wrote Sunday in a letter to colleagues, who had been expected to be out of session until September. "Lives, livelihoods and the life of our American Democracy are under threat from the president."

At an event in Kentucky on Monday, Senate Majority Leader Mitch McConnell distanced himself from Trump's complaints about mail operations. But he also declined to recall senators to Washington, vowing the Postal Service "is going to be just fine."

"We're going to make sure that the ability to function going into the election is not adversely affected," McConnell said in Horse Cave, Ky. "And I don't share the president's concerns."

On Monday, two lawmakers called on the FBI to investigate whether DeJoy or members of the Postal Board of Governors may have committed a crime in slowing the mail.

Rep. Ted Lieu, D-Calif., and Rep. Hakeem Jeffries, D-N.Y., cited reports that mail-sorting machines were being dismantled and policy changes have delayed mail delivery.

"It is not unreasonable to conclude that Postmaster General DeJoy and the Board of Governors may be executing Donald Trump's desire to affect mail-in balloting," they wrote in the letter to FBI Director Christopher Wray.

Congress is at a standoff over postal operations. House Democrats approved funds as part of a pending COVID-19 relief package but Trump and Senate Republicans have balked at additional funds for election security. McConnell held a conference call Monday with Treasury Secretary Steven Mnuchin and GOP senators on the broader virus aid package.

On Sunday, Democratic lawmakers demanded that leaders of the Postal Service testify at an emergency House Oversight and Reform Committee hearing on Aug. 24 on the delays.

The agency did not immediately respond to requests for comment, but said Sunday it would stop removing its distinctive blue mailboxes through mid-November following complaints from customers and members of Congress that the collection boxes were being taken away.

"Given the recent customer concerns the Postal Service will postpone removing boxes for a period of 90 days while we evaluate our customers' concerns,'' Postal Service spokeswoman Kimberly Frum said.

The legislation being prepared for Saturday's vote, the "Delivering for America Act," would prohibit the Postal Service from implementing any changes to operations or level of service it had in place on Jan. 1.

DeJoy, a major Republican donor and ally of the president who took control of the agency in June, has pledged to modernize the money-losing agency to make it more efficient, and eliminated most overtime for postal workers, imposed restrictions on transportation and reduced of the quantity and use of mail-processing equipment.

Trump said last week that he was blocking a $25 billion emergency injection sought by the Postal Service, as well as a Democratic proposal to provide $3.6 billion in additional election money to the states. The money for the post office is intended to help with processing an expected surge of mail-in ballots. Both funding requests have been tied up in congressional negotiations over a new coronavirus relief package.

The president's critics contend that Trump has made the calculation that a lower voter turnout would improve his chances of winning a second term.

"What you are witnessing is a president of the United States who is doing everything he can to suppress the vote, make it harder for people to engage in mail-in balloting at a time when people will be putting their lives on the line by having to go out to a polling station and vote," said Sen. Bernie Sanders, I-Vt.

In announcing the upcoming hearing, congressional Democrats said in a statement: "The postmaster general and top Postal Service leadership must answer to the Congress and the American people as to why they are pushing these dangerous new policies that threaten to silence the voices of millions, just months before the election."

Funding a cash-strapped Postal Service has quickly turned into a top campaign issue as Trump presses his unsupported claim that increased mail-in voting will undermine the credibility of the election and Democrats push back.

The president's chief of staff, Mark Meadows, tried on Sunday to counter criticism that Trump was trying to stifle turnout with national and battleground state polls showing him facing a difficult path to reelection against Biden.

"I'll give you that guarantee right now: The president of the United States is not going to interfere with anybody casting their vote in a legitimate way, whether it's the post office or anything else," Meadows said.

But Democrats said changes made by DeJoy constitute "a grave threat to the integrity of the election and to our very democracy."

The agency in the meantime is now seeking a short-term, end-of-the-year rate increase, according to a notice filed Friday with the Postal Regulatory Commission. The reasons: increased expenses, heightened demand for online packages due to the coronavirus pandemic and an expected increase in holiday mail volume.

The plan would raise prices on commercial domestic competitive parcels, including Priority Mail Express, Priority Mail, first-class package service, Parcel Select and Parcel Return Service.

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Associated Press writers Darlene Superville and Jill Colvin in Washington, Bruce Schreiner in Frankfort, Ky., and Aamer Madhani, reporting from Bedminster, New Jersey, contributed to this report.