A handful of Senate Democrats have yet to commit to confirming Su, who stepped in as acting secretary after Marty Walsh left the Labor Department’s top job in mid-March to take over as head of the NHL players’ union.

Sen. Tammy Duckworth (D-Ill.), one of Su’s chief proponents, downplayed concerns about her confirmation, saying her endorsement from Walsh, who was popular with some Republicans, and meetings with senators will help convince moderates to vote for her.

“She’s doing the best job of the whole thing, which is she’s sitting down and making herself available and she’s had a very good meeting with a large number of” senators, Duckworth said in an interview. “And so I think it’s progressing very nicely.”

Duckworth added: “I think she’s making the case for herself. And I think Marty Walsh coming out as strongly as he has in support of her work, is a very helpful voice to have out there.”

Su told the Senate Health, Education, Labor and Pensions Committee, which is weighing her nomination, she would be an honest broker in the job.

“I have been a leader dedicated to finding and expanding the vast areas of common ground between employers and employees,” she said. “I believe that the Department of Labor should make it as easy as possible for employers to keep workers safe on the job.”

Business groups have targeted Su, fearful that she would pursue regulations that would have major ramifications for app-based companies like Uber and Lyft, franchise restaurants and other employers. The gig-job companies, for instance, are battling efforts to make it easier to reclassify some workers as as employees, which would strain their business models.

Sen. Bernie Sanders (I-Vt.), who chairs the Senate committee considering Su’s nomination, cited that industry pressure in his opening remarks Thursday praising Su.

“The debate over Ms. Su really has nothing to do with her qualifications,” he said. “This debate really has everything to do with the fact that she is a champion of the working class in this country.”

Republicans spent much of Thursday’s hearing trying to poke holes in Su’s record at the Labor Department and as a top labor official in California before that, hoping to crack Democratic unity.

Republicans hammered Su for her stewardship of California’s unemployment insurance system, which issued tens of billions in wrongful or fraudulent payments in the early months of the Covid-19 pandemic. As labor secretary, Su would be in charge of the federal-state partnership on UI.

“The buck stops at the top,” Sen. Mitt Romney (R-Utah) said. “You’re the person running UI, you’re the one who decided to waive the guardrails … the idea of promoting a person who’s had that experience to a position of leadership of the entire Department of Labor makes no sense at all.”

GOP senators also pressed Su for regulatory commitments on independent contractor and joint employer regulations. Su reiterated the Labor Department’s position that it does not have the authority to impose a test similar to California’s controversial “ABC” test for whether a worker is an employee or not and said that the department does not plan to pursue a joint employment rule, which could make companies like fast-food chains liable for violations at their franchises.

“There’s not a joint-employer rule on our regulatory agenda,” Su said, adding that she understands the value of the franchise model given her family’s experience running a pizza shop after immigrating from China.

Republicans also criticized her for a relative lack of experience brokering collective bargaining negotiations — a specialty of Walsh’s — a move geared at sowing doubts among the undecided cohort that includes Sens. Jon Tester (D-Mont.), Kyrsten Sinema (I-Ariz.), Mark Kelly (D-Ariz.) and Joe Manchin (D-W.Va.).

Su’s nomination is a high-stakes test for Sanders, who took the committee’s gavel in January, as well as the White House, which has at times struggled to shepherd labor nominees through the narrowly divided Senate.

The HELP committee has scheduled a confirmation vote for Su next Wednesday, which would clear the way for a final floor vote later in the year.

Kelly and Tester both said Thursday they’re still undecided on whether they will support her for the position, with Tester saying that he plans to meet one-on-one with Su next week “hopefully.”

Democrats’ calculus is further complicated by the ongoing absence of Sen. Diane Feinstein (D-Calif.), who is recovering from shingles and has not been in Washington for several weeks.

When asked about any concerns to get Su confirmed, Senate Majority Leader Chuck Schumer dodged the question and said: “She’s a great nominee and we’re working hard to get her confirmed.”

Su has won the support of some business groups, such as the Los Angeles Chamber of Commerce, but her strongest support comes from labor unions and organizations representing Asian Americans and Pacific Islanders. If confirmed, Su would be Biden’s first AAPI Cabinet secretary and join three other AAPI Cabinet members.

Unions have recently begun stepping up their efforts on behalf of Su. The AFL-CIO is rolling out a six-figure campaign that includes ads in D.C. and Arizona — home to Kelly and Sinema, both of whom voted to confirm Su as deputy secretary but are on the fence — and is considering whether to expand to other states.

“This is the time for them to show who they stand with: Is it workers, or is it big corporations?” AFL-CIO President Liz Shuler told reporters Wednesday. “If you voted for her as deputy secretary, the only thing that’s changed is that she has actually more experience and more expertise.”