The House Judiciary and Oversight and Government Reform committees’ investigation into possible bias among top Department of Justice and FBI officials appears to rely on an invalid subpoena, five previous House general counsels wrote in a letter to the leaders of the Judiciary Committee.

That would jeopardize any court proceedings that could arise from it — including charging Deputy Attorney General Rod Rosenstein for contempt of Congress, a threat issued in July by House Freedom Caucus Chairman Mark Meadows of North Carolina.

Meadows, Rep. Jim Jordan of Ohio, and others on the Judiciary and Oversight and Government Reform Committees have threatened Rosenstein with a contempt charge for not complying with the committee’s subpoena to turn over documents related to the DOJ and FBI 2016 investigations into Hillary Clinton’s use of a private email server while she was the secretary of State and possible ties between Donald Trump’s 2016 campaign and Russia.

But a court would likely throw out such a charge because of problems with how the subpoena underlying the Republicans’ investigation was issued, wrote the former general counsels, who served while both Republicans and Democrats controlled the chamber.

“Based on our review of the relevant law and case law, we believe the Final Subpoena may not be valid because it appears not to have been issued in compliance with Judiciary Committee Rules,” the five former general counsels wrote in a letter Friday to Chairman Bob Goodlatte of Virginia and ranking member Jerrold Nadler of New York.

By committee rules, Goodlatte, as chairman, can unilaterally issue a subpoena. But at least two days before he does that, he must “consul[t] with the Ranking Member” by “provid[ing] a full copy of the proposed subpoena, including any proposed document schedule.”

But Goodlatte gave Nadler a “Draft Subpoena” to review before he submitted the “Final Subpoena” ordering Rosenstein to turn over the requested documents.

Those two versions of the subpoena varied in a handful of ways that “appear to be material,” the counsels wrote.

The draft subpoena Nadler received listed 14 categories of document demands; the final subpoena trimmed that number down to nine.

The draft subpoena did not demand any documents related to the Clinton Foundation, Bill and Hillary Clinton’s charitable organization; the final subpoena included an “entirely new category” of document demands pertaining to the Clinton Foundation.

The draft subpoena demanded that Rosenstein turn over documents provided by the DOJ to its Office of Inspector General for its probe, but the final subpoena expanded the scope of that demand to include all documents provided to the OIG regardless of their source, not just documents from the DOJ itself.

And, finally, the draft subpoena demanded documents of communications between certain officials at the DOJ and FBI between January 1, 2016, and November 8, 2016 — the date of the election that year; the final subpoena demanded those same kinds of communications, but did not limit their scope to the timeline stated in the draft subpoena.

If the House voted to hold Rosenstein in contempt for not complying with the subpoena to turn over documents, the case would then be kicked over to the courts, where, the former general counsels wrote, the judge “likely would conclude that the Committee did not follow its rule, thereby invalidating the Final Subpoena.”

A House Judiciary Committee aide said Goodlatte followed proper procedures for consultation for the committee’s subpoena.

Several items from the initial subpoena were combined into one “because the documents in question were all in the possession of the Inspector General and therefore there was no reason to break those requests down individually — the content was the same,” the aide said in a statement Monday.

The Judiciary Committee aide argued that Rosenstein, at the hearing in June, “brushed aside” the notion that the DOJ would not comply with the documents request based on the subpoena’s legitimacy.

Rosenstein testified it “doesn’t matter” to him whether the subpoena is valid — the DOJ would try to “accommodate Congress by providing” the requested documents regardless of the subpoena’s legal legitimacy.

Rosenstein’s comments came weeks before Meadows stepped up his pressure on the deputy AG by filing a resolution of impeachment against him and later threatening to hold him in contempt of Congress.

“We have nothing to add to the DAG’s testimony on this,” a spokesman for the DOJ said in an email Monday.

A spokesman for Nadler called the Republicans’ investigation “reckless.”

“In their zeal to undermine the Justice Department and [special counsel Robert S. Mueller III’s] criminal investigation, House Republicans have pursued a reckless investigation with real consequences for the rule of law,” Daniel Schwarz, Nadler’s spokesman, said in a statement.

“This letter shows that the subpoena that would be used to hold the Deputy Attorney General in contempt was defective from the outset,” the spokesman said.

Nadler previously raised the issue of the invalid subpoena with Goodlatte in a letter dated June 21 of this year.

Goodlatte’s March 22 subpoena, one of three subpoenas he has issued unilaterally this year, “does not comply with Committee rules and is therefore not a valid subpoena under the Rules of the House,” Nadler wrote.

Nadler noted that he had discussed on another occasion with Goodlatte that the requisite “consultation” was not complete until the chairman gave him the final subpoena to review.

The former general counsels’ assessment could be a procedural obstacle for House GOP investigators and stall an investigation that is in its sixth month, though they could plow ahead with the probe and subpoena until challenged in court.

Meadows suggested before the August recess that House Speaker Paul D. Ryan was on board with the plan to move forward with contempt proceedings this month if the DOJ was not in compliance with Congress’ document request.

“The speaker is willing to support Chairman Goodlatte in a contempt process if the agreed upon documents are not delivered,” he said.

But while Meadows, Jordan, and others have cried foul on Rosenstein for dragging his feet to comply with the document request, Ryan and Goodlatte have said the DOJ is moving at an appropriate pace handing over the documents.

The investigation into bias among top-ranking officials at the DOJ and FBI initially arose after House Permanent Select Intelligence Committee Chairman Devin Nunes issued a four-page memo in February in which he claimed that officials at the FBI “may have relied on politically motivated or questionable sources” to obtain Foreign Intelligence Surveillance Act warrants on former Trump campaign aide Carter Page.

The California Republican was referring to an unverified dossier on Trump’s ties to Russia produced by former British intelligence agent Christopher Steele for the political consulting firm Fusion GPS, which was doing opposition research on Trump for Clinton’s presidential campaign.

Intelligence Committee ranking member Adam Schiff of California wrote a “counter-memo” challenging Nunes and the Republicans’ assessment on many statements that Schiff said were false or misleading.

In July, the Justice Department released the four FISA warrants on Page in heavily redacted form. The warrants mostly corroborated Schiff and the Democrats’ assertion that the dossier was only one small element of the FBI’s request for a warrant to monitor Page, who had left the Trump campaign by the time the FBI applied for the warrant.

Democrats on the Judiciary and Oversight Committees have railed against their GOP colleagues for trying to, as Nadler put it last month, “create a distraction and undermine the Department of Justice as a hedge against” what department investigators might find about Trump and his inner circle.

Five of the president’s associates, including his former campaign chairman Paul Manafort, have pleaded guilty to crimes uncovered by Mueller’s special counsel team.

Republicans have pointed to segments in DOJ IG Michael Horowitz’s report in which he concluded that some top officials at the DOJ demonstrated a “willingness to take official action” to prevent a Donald Trump presidency.

Former FBI official Peter Strzok was fired last month after Horowitz reported and House Republicans highlighted his anti-Trump text exchanges with DOJ lawyer Lisa Page, his alleged mistress, in 2016.

But the OIG did not find that Strzok or anyone else it looked as part of its investigation acted upon their political leanings in the Clinton email and Trump-Russia probes, Horowitz wrote.

“We did not find documentary or testimonial evidence that improper considerations, including political bias, directly affected those specific investigative decisions” that the OIG reviewed, Horowitz told the joint Oversight and Judiciary panel in June.

Watch: Jim Jordan and Rod Rosenstein’s Fiery Exchange