A US federal judge Thursday ordered the Trump campaign to provide evidence of voter fraud in Pennsylvania’s vote-by-mail election system.

Thursday’s order requires the campaign to submit evidence to the court by Friday. Judge Nicholas Ranjan of the US District Court for the Western District of Pennsylvania stated that the “Court finds that instances of voter fraud are relevant to the claims and defenses in this case. … [I]f they have none, state as much.”

The order is part of the ongoing court legal battle between President Donald Trump’s 2020 election campaign and Pennsylvania Secretary of State Kathy Boockvar. The campaign alleges that Pennsylvania mail-in voting will undermine the integrity of the election by allowing for invalid votes to be cast.

“[Boockvar’s] hazardous, hurried, and illegal implementation of unmonitored mail-in voting which provides fraudsters an easy opportunity to engage in ballot harvesting, manipulate or destroy ballots, manufacture duplicitous votes, and sow chaos,” the campaign asserted in its June complaint.

Fact-checkers, researchers and journalists have repeatedly denied claims of widespread voter fraud in mail systems as meritless. Pennsylvania Democrats claim that the lawsuit is merely an attempt by the president to raise an inaccurate and false alarm about the validity of mail-in voting.

Earlier this week, Trump said in an interview that he is refusing additional funding to the post office because such appropriations would enable the agency to conduct universal mail-in voting. Former President Barack Obama criticized Trump’s position as an attempt to suppress the vote and urged citizens to cast ballots early in this year’s election.

A hearing about evidence of voter fraud will be held in September.