Republican lawmakers sharply criticized Thomas Perez, the nominee for labor secretary, in a report Sunday over what they said was a questionable deal he brokered while serving as head of the Justice Department’s Civil Rights Division.

The 63-page report, issued after months of investigation, is certain to provide fodder for Republicans seeking to challenge Perez at his Senate confirmation hearing Thursday.

The GOP lawmakers accuse Perez of misusing his power last year to persuade the city of St. Paul, Minn., to withdraw a housing discrimination case before it could be heard by the Supreme Court. In exchange, the Justice Department agreed not to intervene in two whistleblower cases against St. Paul that could have won up to $200 million for taxpayers.

Perez has defended his reason for wanting St. Paul to drop its case, telling investigators that he feared an adverse ruling from the Supreme Court would jeopardize the government’s use of statistics to win housing discrimination cases. The Justice Department also says Perez got proper clearance and made the deal in the best interests of the nation.

But Republicans say the deal was dubious, that Perez misled senior officials about his intentions and that he tried to cover up the true reason for his decision not to intervene in the whistleblower cases. “This offer was inappropriate and potentially violated Perez’s duty of loyalty to his client, the United States,” said the report from Sen. Charles E. Grassley, California Rep. Darrell Issa (Calif.) and Rep. Bob Goodlatte (Va.). Issa is chairman of the House Oversight Committee, and Goodlatte heads the House Judiciary Committee. Grassley is top Republican on the Senate Judiciary Committee.

Top Democrats on the House Oversight Committee issued a report on the investigation Sunday, writing that Perez “acted professionally to advance the interests of civil rights and effectively combat the scourge of housing discrimination.” The Justice Department also defended Perez, saying litigation decisions made by the department “were in the best interests of the United States and were consistent with the department’s legal, ethical and professional responsibility obligations.”

The GOP report cites documents that suggest Perez’s decision frustrated and confused career lawyers at Justice who initially wanted to join the whistleblower cases against St. Paul. These lawyers described the department’s change of heart as “weirdness,” “ridiculous” and a case of “cover your head pingpong.”

Democrats say Perez was up front about using the strategy and cleared it with ethics and professional responsibility officials before it was finalized. Associate Attorney General Thomas J. Perrelli told investigators that it was common Justice Department practice to encourage parties not to pursue Supreme Court cases with poor fact patterns that could lead to adverse national interests.

“Instead of identifying inappropriate conduct by Mr. Perez, it appears that the accusations against him are part of a broader political campaign to undermine the legal safeguards against discrimination that Mr. Perez was protecting,” said the staff memo issued Sunday by Rep. Elijah E. Cummings (Md.), top Democrat on the House Oversight Committee, and Rep. John Conyers Jr. (Mich.), top Democrat on the House Judiciary Committee.

— Associated Press