U.S. House Republicans sought testimony on Thursday from more than a dozen officials from the Justice Department, FBI and other government agencies involved in the federal tax investigation of President Joe Biden’s son, Hunter.

Three Republican committee chairs in the House of Representatives said the testimony is necessary in light of allegations by Internal Revenue Service whistleblowers that the DOJ intervened in the tax probe to protect the president’s son.

U.S. Attorney General Merrick Garland last week denied the whistleblower allegations, saying that the prosecutor appointed by Republican former President Donald Trump who is leading the investigation was given complete authority to make charging decisions.

House Republicans have long made investigations of the president, his family and his administration a top priority. Partisan calls for action have intensified since Trump was indicted on criminal charges for mishandling classified government documents.

Republican House Speaker Kevin McCarthy warned earlier this week that Garland could face impeachment over the whistleblower allegations.

Thursday’s testimony requests came from House Judiciary Committee Chairman Jim Jordan, House Oversight Committee Chairman James Comer and House Ways and Means Committee Chairman Jason Smith.

“The committees seek to examine whistleblower claims that the … investigation of Hunter Biden was purposely slow-walked and subjected to improper and politically motivated interference,” they said in a letter to Garland.

A Justice Department spokesperson confirmed receiving the letter and declined further comment.

Hunter Biden has agreed to plead guilty to two misdemeanor charges of willfully failing to pay income taxes and to enter as part of an agreement that could avert conviction on a gun-related charge, according to court documents filed last week.