WASHINGTON — Back­lash mount­ing, Pres­i­dent Don­ald Trump’s embat­tled Post­mas­ter Gen­er­al Louis DeJoy will appear Fri­day before the Sen­ate to tes­ti­fy on mail deliv­ery delays and ser­vice changes that law­mak­ers and oth­ers are warn­ing could imper­il the Novem­ber election.

Trump has flat­ly denied he was ask­ing for a slow-walk of the mail. But his new­ly-installed post­mas­ter, a Repub­li­can donor with no pre­vi­ous postal man­age­ment, is fac­ing pres­sure by Democ­rats to halt any changes as mil­lions of Amer­i­cans pre­pare to vote by mail dur­ing the COVID-19 cri­sis. Demon­stra­tions are being held Tues­day in sev­er­al cities.

Key Repub­li­cans are now sound­ing the alarm.

In the piv­otal swing state of Ohio, Attor­ney Gen­er­al Dave Yost plead­ed with Trump to post­pone any need­ed changes to the Postal Ser­vice until after Elec­tion Day. GOP Sen. Rob Port­man and oth­er Repub­li­cans in Ohio’s con­gres­sion­al del­e­ga­tion urged DeJoy to “ensure time­ly and accu­rate deliv­ery of elec­tion-relat­ed materials.”

The cri­sis at the Postal Ser­vice has erupt­ed as a major elec­tion year issue as DeJoy, a Trump ally who took con­trol of the agency in June, has swift­ly engi­neered cuts and oper­a­tional changes that are dis­rupt­ing mail deliv­ery oper­a­tions and rais­ing alarms among workers.

At the White House, Trump lev­eled fresh assaults Tues­day on mail-in vot­ing and uni­ver­sal bal­lots. More Amer­i­cans than ever are expect­ed to choose to vote absen­tee this year instead of risk­ing health con­cerns by vot­ing at polling places dur­ing the coro­n­avirus outbreak.

“You can’t have mil­lions and mil­lions of bal­lots sent all over the place, sent to peo­ple that are dead, sent to dogs, cats, sent every­where,” Trump told reporters.

“This isn’t games and you have to get it right,” Trump said.

Trump made clear last week that he was block­ing $25 bil­lion emer­gency aid to the Postal Ser­vice, acknowl­edg­ing he want­ed to cur­tail elec­tion mail oper­a­tions, as well as a Demo­c­ra­t­ic pro­pos­al to pro­vide $3.6 bil­lion in addi­tion­al elec­tion mon­ey to the states to help process an expect­ed surge of mail-in ballots.

Con­gress is not in ses­sion but Speak­er Nan­cy Pelosi is call­ing the House back to Wash­ing­ton over the cri­sis at the 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.

The House is expect­ed to vote Sat­ur­day on leg­is­la­tion that would pro­hib­it changes at the agency. The pack­age will also include $25 bil­lion to shore up the Postal Ser­vice, which faces con­tin­ued finan­cial losses.

DeJoy and the head of the Postal Ser­vice board of gov­er­nors are also set to tes­ti­fy Mon­day in the House.

“We have to save the Post Office from the Pres­i­dent now,” Pelosi said late Mon­day on MSNBC.

The top Demo­c­rat on the Home­land Secu­ri­ty pan­el seek­ing DeJoy’s tes­ti­mo­ny, Sen. Gary Peters of Michi­gan, called the Postal Ser­vice “a life­line” to Americans.

“We must ensure they can con­tin­ue to count on depend­able and time­ly deliv­ery,” said Peters.

The Postal Ser­vice is among the nation’s old­est and more pop­u­lar insti­tu­tions, strained in recent years by declines first-class and busi­ness mail, but now hit with new chal­lenges dur­ing the coro­n­avirus pan­dem­ic. Trump rou­tine­ly crit­i­cizes its busi­ness mod­el, but the finan­cial out­look is far more com­plex, and includes an unusu­al require­ment to pre-fund retiree health ben­e­fits that advo­cates in Con­gress want to undo.

Ahead of the elec­tion, DeJoy, a for­mer sup­ply-chain CEO who took over the Postal Ser­vice in June, has sparked nation­wide out­cry over delays, new prices and cut­backs just as mil­lions of Amer­i­cans will be try­ing to vote by mail and polling places dur­ing the COVID-19 crisis.

Trump has defend­ed DeJoy, but also crit­i­cized postal oper­a­tions and claimed that uni­ver­sal mail-in bal­lots would be “a disaster.”

Experts say exam­ples of bal­lot fraud have been over­stat­ed. The Bren­nan Cen­ter for Jus­tice in 2017 ranked the risk of bal­lot fraud at 0.00004% to 0.0009%, based on stud­ies of past elections.

Sen­ate Major­i­ty Leader Mitch McConnell, who sent sen­a­tors home for a sum­mer recess, dis­tanced him­self Mon­day from Trump’s com­plaints about mail oper­a­tions. But the Repub­li­can leader also declined to recall sen­a­tors to Wash­ing­ton, vow­ing the Postal Ser­vice “is going to be just fine.”

Sen­ate Demo­c­ra­t­ic leader Chuck Schumer and oth­er Democ­rats, mean­while, urged the postal board to use author­i­ty under a 1970 law to reverse oper­a­tional changes put in place last month by DeJoy. If he declines to coop­er­ate, “you have the author­i­ty, under the Postal Reor­ga­ni­za­tion Act, to remove the post­mas­ter gen­er­al,” the sen­a­tors said in a let­ter to board members.

The Postal Ser­vice said it has stopped remov­ing mail­box­es and mail-sort­ing machines fol­low­ing com­plaints from law­mak­ers and cus­tomers. It said it would stop remov­ing its dis­tinc­tive blue mail­box­es through mid-November.

The leg­is­la­tion set 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. The pack­age would include the $25 bil­lion approved as part of the COVID-19 res­cue that is stalled in the Senate.

DeJoy, the first post­mas­ter gen­er­al in near­ly two decades who was not a career postal employ­ee, has pledged to mod­ern­ize the mon­ey-los­ing agency to make it more effi­cient. He elim­i­nat­ed most over­time for postal work­ers, imposed restric­tions on trans­porta­tion and reduced of the quan­ti­ty and use of mail-pro­cess­ing equipment.

Mean­while, the Postal Ser­vice is seek­ing a short-term rate increase that would raise prices on com­mer­cial domes­tic com­pet­i­tive parcels, includ­ing Pri­or­i­ty Mail Express, Pri­or­i­ty Mail, first-class pack­age ser­vice, Par­cel Select and Par­cel Return Ser­vice. The agency cit­ed increased expens­es, height­ened demand for online pack­ages due to the coro­n­avirus pan­dem­ic and an expect­ed increase in hol­i­day mail volume.

Postal work­ers are increas­ing­ly wor­ried about their abil­i­ty to deliv­er for the fall election.

In a let­ter to postal staffers last week obtained by The Asso­ci­at­ed Press, DeJoy said his poli­cies have brought “unin­tend­ed con­se­quences that impact­ed our over­all ser­vice lev­els,” but added that the Postal Ser­vice “must make a num­ber of sig­nif­i­cant changes which will not be easy, but which are necessary.”

Nate Cas­tro, a postal staffer and union shop stew­ard in Flori­da with more than three decades of expe­ri­ence, said the ratio­nale behind DeJoy’s pol­i­cy changes has been unclear.

“He’s on express mode where he’s not even tak­ing the advice of peo­ple that are expe­ri­enced for years,” said Castro.

Asso­ci­at­ed Press writ­ers Antho­ny Iza­guirre in Charleston, W.Va., Kevin Frek­ing, Dar­lene Superville and Jill Colvin in Wash­ing­ton and Bruce Schrein­er in Frank­fort, Ky., con­tributed to this report.