The U.S. Postal Service (USPS) on-time delivery rates for first-class mail remain below previous levels in 59 of the 67 U.S. postal districts, according to Sen. Gary Peters (D-Mich.), who called on Postmaster General Louis DeJoy to take steps to improve service as millions of Americans prepare to mail their 2020 election ballots.

“Delivery performance has fluctuated in recent weeks, and declined overall during the month of September,” Peters said in a statement, while acknowledging that on-time deliveries have improved after a dip this summer.

“I am troubled to learn of recent and continued mail delays across the nation,” Peters wrote in an Oct. 9 letter to DeJoy (pdf). “With the upcoming general election less than 30 days away, I now write again to request information about steps you are taking, including in response to court orders and demands from Congress, to restore on-time mail delivery and expeditiously process absentee ballots and other election mail.”

Peters, the ranking Democrat on the Homeland Security and Governmental Affairs Committee, was one of numerous lawmakers to take USPS to task after operational changes to the Postal Service introduced during the summer led to drops in on-time delivery.

According to an Oct. 8 performance report from USPS, 86 percent of first-class mail was delivered on time in the week of Sept. 26 through Oct. 2. That’s up 1.14 percent from the week prior, but remains below the rate of 90.6 percent before DeJoy’s changes took effect in July. It also lags the nearly 89 percent rate at the beginning of September.

“I urge you to work diligently to eliminate these delays and return service performance immediately to its target levels. USPS should use any resources necessary to achieve this goal,” Peters wrote in the letter.

In its performance report, USPS noted that nearly 98 percent of first-class mail was delivered within two days of the initial estimated delivery date.

Following a hearing before the Senate Homeland Security and Governmental Affairs Committee, DeJoy announced that some of the actions causing concern would be put on hold until after the November election.

As part of the effort to support timely election mail delivery ahead of November’s vote, DeJoy authorized additional resources to satisfy the expected surge in demand.

“The U.S. Postal Service’s number one priority between now and the November election is the secure, on-time delivery of the nation’s election mail. The Postal Service, our unions, and the more than 630,000 postal employees are united in delivering on this sacred duty,” DeJoy said in a statement. “These actions ensure additional resources will be made available as needed to handle whatever volume of election mail we receive.”

The additional resources include expanded processing procedures, extra transportation, extra delivery and collection trips, and overtime, USPS said in a preparedness fact sheet (pdf).

Meanwhile, responding to concerns that Amazon Prime Day deliveries could overwhelm the post office and have a disruptive impact on other mail deliveries, a USPS spokesman in Dallas said it wouldn’t be a problem.

“The U.S. Postal Service has the capacity to flex its nationwide processing and delivery network to meet surges in volume of mail and packages,” Albert Ruiz said, according to Fox 61.

Officials cited by The Washington Post said that USPS has already delivered in this election cycle a record 417 million pieces of election mail, including 64 million ballots. During the 2016 election cycle, there were roughly 200 million pieces of election mail distributed.