The US Postal Service has legal authority to set binding national rules for mail-in ballots

From the articleSupreme Court halts Trump's proposed limits on mail ballots for this year's electionsAlso in Supreme Court says Trump can’t enforce new mail-in ballot regulation, Can you still vote by mail? How Supreme Court ruling impacts voters, The Supreme Court rejects Trump's mail voting restrictions for this year's midterms, Supreme Court rejects Trump mail ballot restrictions ahead of midterms