The Postal Service has warned states that it may not be able to meet their deadlines for delivering last-minute mail-in ballots, another development in a growing controversy over the new postmaster general’s handling of vote-by-mail operations as President Donald Trump continues to rail against the practice.

In letters sent in July to states across the country — including electoral battlegrounds like Pennsylvania, Florida and Michigan — Thomas J. Marshall, general counsel for the Postal Service, warned that “certain deadlines for requesting and casting mail-in ballots are incongruous with the Postal Service’s delivery standards.”

As many states turn to vote-by-mail operations to carry out elections safely amid the coronavirus pandemic, Marshall urged them to require residents request ballots at least 15 days before an election — rather than just the four days allowed under some state laws.

“This mismatch creates a risk that ballots requested near the deadline under state law will not be returned by mail in time to be counted,” Marshall wrote.

Many states have long allowed voters to request a mail ballot close to the election — only one, Rhode Island, meets the standard now being suggested by the Postal Service — but the Postal Service suggested that the large volume of voting by mail at a time of widespread delivery delays meant that states would be better off building more time into their systems.

In response to the warning letters, some states, including Pennsylvania and Michigan, have called for extensions on counting late-arriving ballots in the November election.

“We have asked the Legislature to change Michigan law to allow ballots postmarked by Election Day that arrive within a certain window to be counted,” said Tracy Wimmer, a spokeswoman for Michigan Secretary of State Jocelyn Benson.

The increased demand for vote-by-mail operations comes as the Postal Service itself is undergoing cuts to its operations. The new postmaster general, Louis DeJoy, a Republican megadonor and ally of Trump, has argued that he is modernizing the money-losing agency to make it more efficient. Among his moves have been cuts to overtime for postal workers, restrictions on transportation, and the reduction of the quantity and use of processing equipment at mail processing plants.

In June, shortly after DeJoy was selected to lead the agency, union officials received a notice that Postal Service management was removing 671 machines used to sort mail quickly due to a “reduction to letter and flat mail volume.”

In a letter to American Postal Workers Union president Mark Dimondstein, Rickey R. Dean, the contract administrator, wrote that the Postal Service planned to remove 502 delivery bar code sorters, 87 advanced facer canceling systems, 55 flat sorting machines and 27 flat sequencing systems before the end of September.

Mail operations in several battleground states were hit hard by the cuts. On the list for removal were 24 delivery bar code sorters in Ohio, 11 in Detroit, 11 in Florida, nine in Wisconsin, eight in Philadelphia and five in Arizona.