WASHINGTON — Representative Carolyn B. Maloney, Democrat of New York and the chairwoman of the House Oversight Committee, said Monday that she would subpoena Louis DeJoy, the postmaster general, for documents she said he had withheld from Congress related to mail delays and communications with the Trump campaign.
The subpoena is the latest sign of escalating tension between the new postmaster general — an ally of President Trump and Republican megadonor — and leading Democrats, who have accused him of injecting dysfunction into the United States Postal Service before the November election. The changes Mr. DeJoy has instituted have resulted in confusion and coincided with a slowdown in delivery times and a concerted effort by the president to baselessly attack mail-in voting as fraudulent, arguing that it hurts his re-election chances.
In a statement, the Postal Service said it was “surprised and confused” by the committee’s subpoena.
“We will continue to cooperate with the oversight committees in both the House and Senate, and we fully intend to comply with our obligations under the law,” the statement said.
The statement also said mail performance was beginning to improve after suffering declines during Mr. DeJoy’s first months on the job, when he implemented cost-cutting measures, including a more regimented schedule for running mail trucks at specified times. Documents released Monday afternoon by the Postal Service on Monday show an improvement in delivery times, but not a full return to the level of service provided before Mr. DeJoy implemented his changes.
“We are improving service performance while more consistently running our trucks on time,” Mr. DeJoy said in the statement.
For months, members of Congress have sought documents from Mr. DeJoy about delays in election mail, the removal of machinery and how he has chosen to run the agency. Internal documents show some aspects of mail performance had fallen by as much as 8 percent since he took the helm of the agency.
Democrats have raised concerns that Mr. DeJoy is interfering with the mail as part of a broader effort by Mr. Trump to sow distrust in voting by mail ahead of a pandemic-era election in which mail-in ballots will play an outsize role. Among their requests for documents: information about the removal of hundreds of letter-sorting machines and the limiting of overtime — both actions denounced by union officials.
Mr. DeJoy has yet to provide any documents to Congress since a hearing last week of Ms. Maloney’s committee, during which Democrats grilled the postmaster general and some called for him to resign.
Ms. Maloney said she received a letter from Mr. DeJoy on Friday night that said: “I trust my Aug. 24 testimony before the Committee on Oversight and Reform clarified any outstanding questions you had.” In the letter, Mr. DeJoy added that his staff was working on providing materials to the committee, though Ms. Maloney said he had missed last week’s deadline to provide the documents voluntarily.
The subpoena “makes clear as a legal matter that the production of these documents is mandatory,” Ms. Maloney said Monday. She sent a memorandum notifying members of the panel of her plans, meaning the subpoena will most likely be delivered to Mr. DeJoy by Wednesday.
However, the leading Republican on the committee, Representative James Comer of Kentucky, called Ms. Maloney’s move “unilateral” and argued that it broke an agreement between Democrats and Republicans to hold a business meeting before issuing any subpoenas.
“Today’s antics are part of a backwards pattern by the Democrats to promote a baseless conspiracy theory about the Postal Service,” Mr. Comer said. “Instead of allowing the Postal Service to do what it does best — deliver mail to hundreds of millions of Americans — it will now spend hundreds of hours responding to this partisan subpoena,” Mr. Comer said.
In addition to the subpoena, Ms. Maloney said she was requesting documents from Robert Duncan, the chairman of the Postal Service board of governors, who also runs a Republican “super PAC.” Among the documents sought from Mr. Duncan include any communications between board members and the White House and between the board members and Mr. DeJoy.
Ms. Maloney signaled her intention last week to compel the production of documents.
“This committee expects a full and complete production of all the documents we requested no later than this coming Wednesday,” she warned Mr. DeJoy at the hearing last Monday. “And if you continue to withhold information or otherwise fail to comply, you can expect a subpoena.”
Several Democrats urged Ms. Maloney to take such a step.
During one exchange with Mr. DeJoy, Representative Alexandria Ocasio-Cortez, Democrat of New York, sought copies of Mr. DeJoy’s calendar since he started the job on June 15.
“I don’t want to set a precedent for my calendar to be submitted every two months,” Mr. DeJoy objected.
“I would say the details of this calendar are extraordinarily important to the committee’s investigations,” Ms. Ocasio-Cortez told Ms. Maloney. “And if we cannot receive them voluntarily, I would recommend consideration of a subpoena for these details.”
His calendar is now part of the subpoena request.