Rep. Trent Franks, R-Ariz., is calling for the resignation of Robert Mueller, the special counsel for the Russia investigation, and says Mueller has a conflict of interest because he's close friends with former FBI Director James Comey.

Franks, a member of the House Freedom Caucus who sits on the Judiciary Committee, said another major problem is that members of Mueller's team donated to Hillary Clinton's campaign last year.

"Bob Mueller is in clear violation of federal code and must resign to maintain the integrity of the investigation into alleged Russian ties," Franks said. "Those who worked under them have attested he and Jim Comey possess a close friendship, and they have delivered on-the-record statements effusing praise of one another."

"No one knows Mr. Mueller's true intentions, but neither can anyone dispute that he now clearly appears to be a partisan arbiter of justice. Accordingly, the law is also explicitly clear: he must step down based on this conflict of interest," Franks said.

"Already, this investigation has become suspect – reports have revealed at least four members of Mueller's team on the Russia probe donated to support Hillary Clinton for President, as President Trump pointed out. These obviously deliberate partisan hirings do not help convey impartiality," Franks said. "Until Mueller resigns, he will be in clear violation of the law, a reality that fundamentally undermines his role as Special Counsel and attending ability to execute the law."

In recent weeks, the drumbeat from Trump supporters against Mueller has intensified. Some have speculated that Trump may fire Attorney General Jeff Sessions after a series of disparaging statements due in large part to his recusal from the investigation, and push for Mueller's ouster from the investigation.

Trump has repeatedly labeled the investigation a "witch hunt" and has maintained that he committed no wrongdoing.