Lawmakers said during a contentious congressional hearing Thursday they are uneasy about the U.S. Postal Service’s readiness for a crush of mail ballots for the November election because some of them feel burned by other Postal Service actions.

Postmaster General Louis DeJoy sought to reassure a House Appropriations subcommittee that the Postal Service is well-positioned for an extraordinary effort to deliver mail ballots to election officials on time to be counted and that close to 100% will make it promptly. In recent weeks, DeJoy has pushed back on suggestions from state and local election officials that the Postal Service has not addressed problems that led to mail ballots arriving too late or without postmarks.

But as subcommittee members asked DeJoy about how the Postal Service has addressed election officials concerns, they criticized a larger, longer-term plan to make the mail delivery system more efficient and less costly by consolidating mail processing centers, suggesting it could slow mail delivery, particularly in rural areas. DeJoy disputed that.

DeJoy has said repeatedly that the Postal Service’s larger plans won’t affect the handling of potentially tens of millions of mail ballots for the Nov. 5 election because the plan is on hold for October and the first half of November. But subcommittee Chair David Joyce, an Ohio Republican, told him in opening the hearing that broader problems with mail delivery are on constituents’ minds as the presidential election approaches.

“Many of our constituents have expressed concerns about the Postal Service’s ability to deliver election ballots securely and on time,” Joyce said. ”It is imperative that the Postal Service get this right.”

DeJoy told the lawmakers that the Postal Service’s 650,000 employees will be sifting through 300 million pieces of mail to capture stray ballots and ensure they arrive on time. He said the Postal Service has improved its training.

“We’re doing very well at this — just not perfect,” he said.