U.S. District Judge Trevor N. McFadden of the District of Columbia.

A federal judge in Washington, D.C., on Tuesday abruptly halted the House's lawsuit seeking President Donald Trump's federal tax returns pending an appeals court ruling on whether former White House counsel Don McGahn can be compelled to testify.

U.S. District Judge Trevor McFadden of the District of Columbia at 2:54 p.m. Tuesday scheduled a phone conference in the case for 3 p.m. Shortly afterward, an order was issued saying the case will be stayed until the U.S. Court of Appeals for the D.C. Circuit issues its decision in the McGahn case.

The three-judge panel on the D.C. Circuit heard arguments in that case Jan. 3. The appellate court is scheduled to release opinions Friday, although it's unclear when a ruling will be made.

Why McFadden, who Trump appointed to the bench in 2017, is concerned about the McGahn case is currently only known to the judge and lawyers on the call.

Both the McGahn and tax returns lawsuits seek to enforce congressional subpoenas for information relating to the president, but there are few other similarities between the two cases.

House lawyers say McGahn was privy to potential acts of obstruction of justice by Trump, as laid out in special counsel Robert Mueller's report. Democrats want his testimony for the Senate's impeachment trial, set to begin in earnest next week, and haven't ruled out the possibility of the testimony being used for additional articles of impeachment against the president.

The House Ways & Means Committee, which is behind the Trump tax returns lawsuit, requested the documents last year under a provision in the tax code that allows the committee to request returns from the IRS.

Treasury Secretary Steve Mnuchin denied that request, as well as a subpoena for the returns, saying they lacked a "legitimate legislative purpose." The committee went to court shortly after that.

McFadden has wrestled in the past over other House lawsuits. He dismissed lawmakers' lawsuit last year over Trump's diversion of military funds for a border wall, saying he didn't believe the House had standing to sue.

And after Trump's personal attorneys moved for McFadden to hear their lawsuit challenging a New York law that would let lawmakers access Trump's state returns, the judge found that it wasn't related to the House suit seeking the president's federal returns and didn't belong in his court.

University of Iowa law professor Andy Grewal said McFadden's order "seems like the prudent course."

"Whether the Ways & Means Committee has standing to sue the IRS is an open question, and the McGahn case may shed light on it," he tweeted.

McFadden heard oral arguments in the House tax returns case in November, during which he indicated he thought the House did have standing to sue.

But standing remained a major topic during the D.C. Circuit's arguments over McGahn's testimony earlier this month.

Justice Department attorney Hashim Mooppan told the judges that they should stay out of the McGahn lawsuit, now that the House has impeached Trump. Mooppan said a court ruling could be viewed as interfering in the impeachment process and could ultimately undermine Americans' trust in the federal judiciary.

Judge Thomas Griffith, who previously worked in the Senate, also suggested during the arguments the House had tools other than going to court to compel McGahn's testimony.

"Cut the appropriations, get the Senate to stop confirming judges," Griffith said. "You're not without remedy here."

House attorney Megan Barbero, a former Justice Department lawyer, argued that even if there are political issues involved in the case, "it is the duty of the court in a case that is otherwise justiciable … to say what the law is."

Read more:

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DOJ Tells 'Unelected and Unaccountable' Judges to Stay Out of Fight for McGahn Testimony

A Judge Didn't Sound Eager to Throw Out House Suit Seeking Trump Tax Returns

DOJ's Legal Counsel Office Picks Up Former US House Lawyer

READ: US House Asks Judge to Force Disclosure of Trump's Taxes