"I think the fact that the personal emails haven't been responded to in the House, in terms of the subpoena, are enough for me to have serious concerns," Sen. Johnny Isakson (R-Ga.) told The Hill.
Sen. Richard Burr (R-N.C.), who said he plans to show up for the vote, said Perez's inability to provide the requested information disqualifies him from getting the Labor job.
"I actually have major concerns about his release of government nonpublic documents and nonpublic information, and there's no indication on his part that he thought there was anything improper with that," he told The Hill.
"And right now, that's a disqualifier unless he clears that up between now and then."
A Senate aide said Republican attendance "may be sparse" because Democrats only need half of the committee to hold the vote.
"There seems to be little Republican support for Perez. Some Republicans have been waiting a long time on information they deem necessary to doing their job of advice and consent, and others have decided on the merits," the aide told The Hill.
Meanwhile, Democratic support for Perez has been unwavering.
Sen. Barbara Mikulski (D-Md.) said she certainly hopes the panel can approve his nomination on Thursday.
"I'm a great admirer of Tom Perez," she said.
"He's done a great job in Maryland and at the Justice Department."
She said support from the Maryland Chamber of Commerce should provide an indication of the strength of his credentials.
"They had some of the reluctance that others had, was he too left, too liberal, too labor," she said.
"That's a starchy group, and they're supporting him. I hope we have a Senate vote."
House and Senate Republicans contend that Perez acted unethically in a deal with city officials in St. Paul, Minn.
They argue he convinced the city to drop a Supreme Court appeal that would have had a potentially adverse effect on discrimination cases in exchange for the Justice Department's agreement to step away from two whistle-blower cases.
Attorney General Eric Holder argued on Wednesday that Perez acted properly in the St. Paul case, took the proper steps to ensure the course of action was "ethically sound," and "it seems to me that what was done was in the best interest of the people of the United States," he said during a House Judiciary Committee hearing.
Holder and House Government Reform and Oversight Committee Chairman Darrell Issa (R-Calif.) faced off over whether Perez acted appropriately.
In trying to respond to Issa, Holder said, “I am not going to stop talking now."
"It is inappropriate and too consistent with the way in which you conduct yourself as a member of Congress," Holder said. "It is unacceptable. It is shameful."
The hold up on Perez's nomination could lead to Senate Majority Leader Harry Reid (D-Nev.) and his Democratic colleagues to more seriously consider launching the "nuclear option" that would disable the 60-vote threshold requirement on certain nominations and allow for a majority vote on the Senate floor.
If the Senate rules are changed, that would probably smooth the process for Perez's contentious nomination and several others that have gotten stuck amid the upper chamber's procedural rules, including Gina McCarthy for the Environmental Protection Agency (EPA), Richard Cordray at the Consumer Financial Protection Bureau and Obama’s picks to sit on the National Labor Relations Board.