House Democrats have formally issued a subpoena for the full contents of Special Counsel Robert Mueller’s report on interference in the 2016 election. It’s the first official step in what will likely become a legal showdown between Congress and the Trump Administration.

Rep. Jerrold Nadler, who chairs the judiciary committee, announced Friday morning that he was sending a subpoena to the Department of Justice for both the un-redacted report and all underlying evidence. The Department of Justice has until May 1 to comply. Although Nadler’s committee is conducting multiple probes of the Trump Administration, this is the first subpoena he has issued since he assumed the gavel in January.

“I am open to working with the Department to reach a reasonable accommodation for access to these materials, however I cannot accept any proposal which leaves most of Congress in the dark, as they grapple with their duties of legislation, oversight and constitutional accountability,” Nadler said in a statement.

The subpoena comes less than 24 hours after Attorney General William Barr released a redacted version of Mueller’s report to both the public and Congress. The report was redacted based on four categories: material from grand jury testimonies, material that could compromise intelligence sources and methods, material relating to current investigations, and “information that would unduly infringe on the personal privacy and reputational interests of peripheral third parties.”

The Justice Department has set up a briefing later in the month for officials with top clearance to view the redacted information. But Congressional Democrats say they should have access to the full report, an argument that reached a fever pitch after Mueller appeared to toss the question of whether President Donald Trump obstructed justice in the investigation to Congress.

“I think it was probably written with the intent of providing Congress a roadmap, as other reports have in the past.” Nadler said on Thursday. “With a lot of the redactions and others Attorney General Barr seems to be trying to frustrate that intent.

Often a subpoena is used as a negotiating tool to coerce both sides to reach an agreement without a court fight. But veterans of past legal showdowns between Congress and the executive branch are confident this one will reach the courts. Experts say the Justice Department can cite legal precedent for withholding some of the materials the Democrats are requesting, like grand jury testimony.

“I would expect that even if the Justice Department decides to provide flexibility on some matters – for instance national security redactions – with respect to grand jury material I am sure they will take the position that they don’t have the discretion to release that information,” said one former House attorney, who requested anonymity given the sensitivity of the matter. “The only way to solve that would be to go to court if the committee wants to get access to that material.”

Write to Alana Abramson at Alana.Abramson@time.com.