WASHINGTON — The Republican chairman of a powerful House committee called for the removal of the IRS commissioner Monday, saying he has obstructed congressional probes into the treatment of conservative groups.

Rep. Jason Chaffetz, R-Utah, sent a letter Monday to President Barack Obama, asking him to remove IRS Commissioner John Koskinen. Chaffetz is chairman of the House Oversight Committee, which has been investigating the IRS for more than two years.

“Throughout his tenure, Commissioner Koskinen obstructed these congressional investigations,” Chaffetz wrote in a letter that was also signed by 20 other Republicans on the Oversight Committee. “His obstruction takes the form of failure to comply with a congressional subpoena, failure to testify truthfully and failure to preserve and produce up to 24,000 e-mails relevant to the investigation.”

Chaffetz also raised the possibility of impeaching Koskinen or voting to hold him in contempt of Congress.

The White House had no comment Monday, but the Treasury Department issued a statement saying Koskinen has Treasury Secretary Jacob Lew’s full confidence. The IRS is part of the Treasury Department.