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

Rep. Jason Chaffetz, R-Utah, sent a letter Monday to President 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. “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 emails relevant to the investigation.”

The White House did not immediately respond to a request for comment.

The IRS issued a statement disputing Chaffetz’s allegations, saying the agency and “Koskinen have been cooperative and truthful with the numerous investigations underway.”

The IRS says more than 1 million pages of documents have been provided to “more than 30 congressional hearings on these issues.”

“The agency will continue to cooperate with the committees, support the important oversight role of Congress as well as make additional improvements in our operations and processes,” the IRS said in a statement.

The Senate confirmed Koskinen as head of the IRS in December 2013, months after the agency acknowledged that agents had mistreated conservative groups when they applied for tax-exempt status. Koskinen, a specialist at turning around troubled agencies and companies, was tasked with restoring trust in an agency that had lost much of its top management to the scandal.

Chaffetz said Koskinen failed to preserve IRS emails by a key figure in congressional investigations, despite promising to produce them.

Last month, the IRS’s inspector general told Congress that two IRS workers at a computer center in West Virginia had erased computer backup tapes that could have contained up to 24,000 emails to and from Lois Lerner, who used to head the IRS division that oversees tax-exempt groups.