PORTLAND, Maine (AP) — Maine U.S. Sen. Angus King, an independent, is warning that changes at the U.S. Postal Service, including a ban on overtime, are harmful to Maine residents and may hamper the agency’s ability to deliver absentee ballots in November.

King called the postal service “no-less-than-vital” in a letter including testimony from his constituents that he sent Thursday to U.S. Sen. Gary Peters of Michigan, the ranking Democrat on the Senate’s Committee on Homeland Security and Government.

Peters also on Thursday launched an investigation into reported delays at the postal service.

King’s warning echos that of 84 House members and at least two senators, who wrote to Postmaster General Louis DeJoy on Thursday and called for him to immediately reverse operational changes that are causing delays in deliveries across the country.

The changes include the elimination of overtime for hundreds of thousands of postal workers and new mandates that mail be kept until the next day if distribution centers are running late.

Postal workers in Maine told King they were harassed if they arrived early or left late even by a few minutes and said a new policy at the post office in Portland instructed workers to prioritize Amazon packages over first class mail.

Allegations that the postmaster in Portland was willfully delaying the delivery of mail were first reported by the Portland Press Herald in July.

“Any attack on or attempt to damage USPS services constitutes a harm to the people I represent,” King wrote.

Postal workers feel personally responsible for their role in delivering ballots during the upcoming presidential election but unsupported by the postal service, King said.

King has been a long time advocate for the postal service, the newspaper reported.