The US Postal Service definitively said Monday that it had the capacity to handle the added volume of mail-in ballots in November’s general election after President Donald Trump questioned its ability to do so.

“The Postal Service has ample capacity to adjust our nationwide processing and delivery network to meet projected Election and Political Mail volume, including any additional volume that may result as a response to the COVID-19 pandemic,” the agency said in a statement.

The agency’s resolute stance comes after high profile naysayers, especially the President, have cast doubt on whether it will be able to handle an election that is expected to see significant numbers of mail-in ballots as the pandemic rages on.

On Monday morning, Trump attacked vote by mail and USPS’ capacity to handle an election where people aren’t voting in person, tweeting that the “Post Office could never handle the Traffic of Mail-In Votes without preparation.”

Later Monday, Trump again slammed mail-in ballots during a press briefing, saying, “How are you going to do that for an entire nation? They’re using Covid to try and get the mail-in ballots.”

“The Post Office for many, many years has been, you know, run in a fashion that hasn’t been great — great workers and everything, but they have old equipment, very old equipment,” Trump added. “And I don’t think the Post Office is prepared for a thing like this. You have to ask the people at the Post Office, but how can the Post Office be expected to handle?”

On Friday, American Post Workers Union President Mark Dimondstein told CNN that new, recently implemented US Postal Service procedures — which have led to delays across the country in mail delivery — could affect mail-in voting for the November election. He said that the union, which represents more than 200,000 Postal Service employees and retirees, has received a number of reports from postal workers and customers over the last two weeks that mail delivery has slowed and “degraded.”

Under the leadership of the new postmaster general, Trump loyalist Louis DeJoy, USPS is seeing a slowing of mail delivery in some places. The agency has recently implemented new efforts that workers blame for delivery delays of at least two days across the country — prompting fears that many ballots may not reach election offices in time if the problems aren’t corrected by November.

In a letter to Congress released Monday, an attorney for USPS argued that an internal memo obtained by CNN advising postal workers of an end to late trips and extra trips did not originate from postal service headquarters and should “not be treated as official statements of Postal Service policy.”

But the letter — dated July 22 and sent in response to a congressional inquiry about service changes at the USPS — does confirm the USPS is taking “immediate steps to increase operational efficiency by re-emphasizing existing operational plans.” It also makes the case that these efforts are “clearly within the legal authority of the Postmaster General” and do not require approval from Congress of the USPS Board of Governors, every member of which is now a Trump appointee.

While the letter does not elaborate on what “steps” the USPS might be taking, it acknowledges there could be an impact on mail delivery, “as with any such management efforts, any temporary service impacts will be monitored and the root causes of any issues will be addressed as necessary and corrected as appropriate.”

In a statement to CNN on Thursday addressing the allegations, a spokesperson said there could be “temporary service impacts,” but any such impacts will be monitored and temporary as the root causes of any issues will be addressed as necessary and corrected as appropriate.” The spokesperson did not refute the changes were being made.

The coronavirus pandemic has accelerated the severity of already problematic finances at the USPS as mail volume has plunged. In April, the USPS told Congress it would be out of money by September and requested $75 billion in emergency funding.

Lawmakers had allocated $25 billion for the USPS in its coronavirus package, the CARES Act, in March, but the Trump administration blocked the funding, instead offering $10 billion in the form of loans and demanding “reforms” must be included as a condition of the loans.

“If they don’t raise the price, I’m not signing anything,” Trump said on April 24.

In a sign of congressional concern over the possibility of delays, the House Oversight Committee on Monday invited DeJoy to testify on September 17.

New York Democratic Rep. Carolyn Maloney, the chairwoman of the panel, wrote she was requesting the testimony “to examine recent changes to U.S. Postal Service operations and standards and the need for on-time mail delivery during the ongoing pandemic and upcoming election, which as you know may be held largely by mail-in ballot.”

USPS did not answer when asked by CNN whether the Postmaster General will appear before the committee as requested on September 17, instead referring all inquiries to the committee.