Rep. Elijah Cummings,  D-Md., the ranking Democrat on the House Oversight and Government Reform Committee, joined Chairman Darrell Issa in demanding that the White House’s nominee to be labor secretary, Thomas Perez, turn over some 1,200 private emails.

The change is notable because Cummings has been an ardent defender of the nominee. He said a House hearing just Tuesday that Republicans had made “partisan and unsubstantiated claims against Mr. Perez.”

Republicans believe Perez, currently the Justice Department’s top civil rights enforcer, used a private email account to conduct official business in an attempt to  circumvent federal transparency laws. Perez has refused to comply with an earlier subpoena to turn over the emails. To date congressional investigators have been allowed to view only 34 of the 1,200

On Wednesday, Cummings told Perez he has to turn the emails over and they must be in “unredacted form” as well. Here’s the text of the letter signed by Issa and Cummings:

We write to request that you produce all documents responsive to the subpoena issued to you by the committee on April 10, 2013, regarding your use of a non-official email account to conduct official Department of Justice business. The Department has represented to the committee that roughly 1,200 responsive emails exist. To allow the committee to fully examine these emails, please produce all responsive documents in unredacted form to the committee no later than Friday, May 10, 2013.

This was the second blow Perez’s nomination suffered this week. He was originally scheduled to appear before the Senate Health, Education, Labor and Pensions Committee on Wednesday for a confirmation vote, but it was abruptly postponed until next week. White House spokesman Jay Carney accused Republicans of  ”obstructionism” for the delay.

Perez has been a controversial choice from the start. He has been a zealous liberal activist in his current job as the Justice Department’s top civil rights enforcer. His Republican critics have been highlighting an unusual quid pro quo deal he arranged with the city of St. Paul, Minn. Perez arranged to get the federal government to drop out of two cases pending against city. One was a whistleblower case involving an estimated $200 million in federal funds.

In exchange, the city dropped a case it was pursuing that could have let the Supreme Court clarify when the legal theory of “disparate impact” could be used in civil rights cases. Perez is a staunch advocate of the theory, which holds that it is not necessary to show an intent to discriminate to prove such a case. Republicans allege Perez tried to hide the fact that he was making the deal from others in the government.