House Oversight and Government Reform Committee Chairman Darrell Issa has subpoenaed the commissioner of the Internal Revenue Service to testify next week before Congress about a trove of lost emails that could contain evidence of a plan to targeted conservative groups.

Issa, R-Calif., will hold a June 23 hearing aimed at finding out more about two year's worth of emails -- from 2009 to 2011 -- that the IRS has reported lost. The emails were from former top IRS official Lois G. Lerner to Justice Department and Treasury officials.

Issa had requested the emails because he and other Republicans believe Lerner played a key role in the targeting scheme and they believe she can link the targeting to even higher levels of the government.

They believe Lerner was conspiring with other administration officials to find a way to target conservative groups seeking tax-exempt status, which Lerner and the Obama administration has denied.

In a tersely worded letter sent Monday to IRS Commissioner John Koskinen, Issa said that the IRS was required under law to preserve the Lerner emails under the Federal Records Act. The IRS, Issa said, is in violation of the law for losing the Lerner emails.

"I will not tolerate your continued obstruction and game-playing in response to the Committee's investigation of the IRS targeting,” Issa wrote to Koskinen. β€œFor too long, the IRS has promised to produce requested β€” and, later, subpoenaed β€” documents, only to respond later with excuses and inaction. Despite your empty promises and broken commitments to cooperation, the IRS still insists on flouting Constitutional congressional oversight."

Agency officials have not indicated yet whether Koskinen will comply with the subpoena.