Special counsel Robert Mueller should testify before Congress “immediately,” to counter “groundless claims” made by Democrats about the inquiry that found no collusion between the Trump campaign and the Russians, a top GOP lawmaker said Monday.

Rep. Doug Collins, R-Ga., who is the ranking member on the House Judiciary Committee, sent a letter to panel chairman Rep. Jerrold Nadler, D-N.Y., calling for Mueller to be invited to testify the week of April 22.

Collins said Attorney General William Barr, who is now under congressional subpoena to produce Mueller’s full report, would be breaking the law if he disclosed all of its contents.

“While he can testify surrounding his decision to provide the Committee with principal conclusions, it is Special Counsel Mueller who is best-positioned to testify regarding the underlying facts and material in which you are so interested,” Collins wrote to Nadler.

The Judiciary Committee, ruled by Democrats, voted last week to subpoena Barr to turn over the entire Mueller report.

Barr has so far produced a four-page summary and has promised Congress he will send a longer report by mid-April.

The law requires grand jury testimony and other information be withheld, however.

Collins, in the letter to Nadler, accused Nadler of ignoring the law and conflating the Mueller report with the Clinton-era investigation by Kenneth Starr, who was compelled at that time to make public all of his findings.

Nadler, Collins wrote, can obtain all the Mueller findings legally by launching impeachment proceedings, but Democrats, he said, are wary of the political consequences of such a move.

“Your decision to make groundless claims and repeatedly threaten to go to court not only distracts from other Committee business but, based on firm legal precedent, will also end — after months, if not years, of litigation — without the Committee receiving the material you say it requires to complete its work,” Collins wrote to Nadler. “If you decline to launch an impeachment inquiry, which is your clear legal path to the grand jury information, I suggest instead inviting Special Counsel Mueller in to testify before the Committee as soon as possible.”

Congress is not in session during the week of April 22. Collins said lawmakers "can agree this business is too important to wait, and Members of the Committee will surely return to Washington at such a critical moment in our country’s history."