Judge Emmet Sullivan issued a nationwide injunction blocking the USPS from following Trump's new mail ballot delivery directives.
The ruling maintains that the proposed regulations violate a 2021 settlement agreement requiring the agency to prioritize election mail.
The administration's order would have required states to surrender voter lists as a condition for the USPS to process their ballots.
Critics argue the executive order could lead to excessive voter purges and unprecedented federal interference in state-run elections.