The U.S. Postal Service is poised to play a critical new role in determining which mail ballots are delivered to voters this fall. If the Supreme Court allows President Trump to move forward with an executive order he issued in March, the agency would screen ballots after they are submitted by election officials and would deliver only those that comply with new rules. Two dozen states have sued to halt the plan, calling it unconstitutional.

Here’s how the process would work, according to notices issued by the Postal Service: Ballot envelopes must comply with three new standards. Envelope designs must be reviewed and approved by the Postal Service. Each ballot envelope must meet specific requirements.

States must create lists of voters who are approved to receive mail ballots and upload the lists to a new Postal Service portal. The Postal Service will deliver mail ballots only to the voters on these lists. Each list must include three key pieces of information for each voter.

States take their mail ballots to a Postal Service facility. Before the mailing is accepted, the service checks to see whether ballot envelopes comply with the new regulations. These bulk mailings can contain tens of thousands of ballots, often in plastic-wrapped pallets. The ballot envelopes must comply with the new design requirements and must have bar codes that match the list of approved mail voters that states submitted to the portal.