The top Democrat on the House Oversight and Government Reform panel is objecting to a plan to call the Internal Revenue Service commissioner to testify for a third time in a matter of weeks, calling it “public harassment of an agency head.”

Rep. Elijah Cummings, D-Md., sent a letter Monday to Chairman Darrell Issa, R-Calif., objecting to a decision to call Commissioner John Koskinen to testify at a hearing on Wednesday. It would be the third time Koskinen appeared before the panel in the past month, Cummings noted.

“Requiring Commissioner Koskinen to testify again this week not only takes him away from the day-to-day duties of operating an agency with 90,000 employees, but it also diverts our Committee from conducting responsible oversight on many key areas that traditionally have been part of our jurisdiction,” Cummings said in the letter.

Issa, who is serving his last term as head of the oversight panel, has summoned Koskinen this week to provide an update to the panel on the investigation into targeting of conservative groups seeking tax exempt status, including the status of missing emails from top IRS officials.

Republicans believe they have been stonewalled by the agency.

Cummings requested Issa instead hold a hearing on one of eleven topics requested in the past by panel Democrats, including fraud by for-profit hospitals, excessive CEO pay, illegal foreclosure abuse and December's credit card security breach at Target.

“Each of these thoughtful requests from Members of our Committee is more worthy than yet another hearing with the IRS Commissioner this month,” Cummings said. “With just 34 legislative days remaining in the 113th Congress -- and your chairmanship -- I urge you to restore the Committee's traditional oversight priorities and work together on a bipartisan agenda our entire Committee can support.”

An Issa spokesman said Cummings has wanted to end the probe into the IRS targeting for a year, despite evidence suggesting wrongdoing by the agency.

”Despite efforts by the Ranking Member to obstruct fact-based oversight, Commissioner Koskinen actually informed the subcommittee that he would be available to testify on this date back on July 3," the spokesman said. "On July 9, he even appeared in front of another Oversight subcommittee despite the fact that the Commissioner – and not the Committee – had asked if he could testify."