The U.S. Postal Service has been swiftly developing a complex screening system for mail-in ballots ahead of this year’s midterm elections, despite ongoing legal wranglings over President Trump’s executive order to restrict voting by mail. The new system, which requires states to tell the Postal Service which voters will be sent ballots so they can be verified before delivery, shows how aggressively the Postal Service is moving to deliver on the president’s directive ahead of the upcoming elections, which could tip the scales of power in Congress.

The agency’s efforts to set up a way to restrict who gets mail ballots, even as the matter is being fought over in the courts, could cause confusion among voters and undermine confidence in the Postal Service as states are close to getting ballots out the door, current and former state officials said. If the new screening system is ultimately put in place, it could jeopardize the ability of people to receive and cast their ballots, they said.

“It impacts not only voters’ ability to vote, but also their faith in a free and fair system that’s equal for all of us who are eligible to vote,” said Kathy Boockvar, a former Democratic secretary of state in Pennsylvania. More than two dozen Democratic state attorneys general and voting rights organizations have challenged Mr. Trump’s order in the courts, arguing it violates the Constitution’s provision giving states the responsibility to run elections.

Despite a court order temporarily barring the Postal Service from implementing the president’s plan, the agency acknowledged on Tuesday that it had continued to develop the portal. A whistle-blower said this week that the screening portal is being developed in a rushed and sloppy manner that could jeopardize voting by mail across the country. Twenty states are set to mail ballots to voters by Sept. 19. The first up is North Carolina, where county election boards will begin sending out absentee ballots on Friday.