The request is the first time Republican lawmakers involved in the impeachment probe have formally asked Democrats to call witnesses, a possible indication they intend to pursue more traditional channels to counter the investigation even as members seek to disrupt the proceedings themselves.

Republicans Jim Jordan, Devin Nunes and Michael McCaul wrote a letter on Wednesday to Democrat Adam Schiff, the chairman of the House Intelligence Committee, demanding to hear from the whistleblower, an employee in the intelligence community whose identity remains unknown.

“As the so-called impeachment inquiry gathers information that contradicts the employee’s allegations, we ask that you arrange for the committees to receive public testimony from the employee and all individuals he or she relied upon in formulating the complaint,” the lawmakers wrote. As members of the minority, House Republicans do not have the authority to call witnesses themselves, unless given the power to do so by the Democratic majority.