WASHINGTON (AP) — President Joe Biden’s nominee for labor secretary, Julie Su, won praise at her Senate hearing Thursday as “a champion of the working class” even as some key Democrats were unwilling to voice support, creating uncertainty about her confirmation prospects.

A handful of moderate Democrats have not publicly stated whether they will vote for Su’s nomination ahead of Thursday’s confirmation hearing before the Senate Health, Education, Labor and Pensions Committee. Biden in February picked Su, a civil rights attorney and the deputy labor secretary, to replace Marty Walsh, the former mayor of Boston, to lead the Department of Labor.

The daughter of an immigrant mother who arrived on a cargo ship, Su would be the Biden administration’s first Asian American to serve in the Cabinet at the secretary level. Biden last month called her proof of the “American dream” and said “she’s committed to making sure that dream is in reach for every American.”

Su tapped into that spirit in her testimony, recounting how her parents were able to claw their way into the middle class through jobs that provided benefits as well as becoming entrepreneurs.

“When he announced my nomination for U.S Secretary of Labor, the president called me ‘the American Dream.’ My parents believed in it, I benefited from it, and I want to do my part to make sure it is a reality for workers across the nation,” Su said.

She was previously confirmed as the deputy labor secretary, but has faced opposition from business groups critical of her record leading California’s labor department. They point to her support of an overturned California law that would have required app-based ride hailing and delivery companies like Uber and Lyft, as well as trucking businesses, to treat their workers as employees, providing benefits like paid sick leave and unemployment insurance, rather than independent contractors.

Su has also faced blame for problems at the California Labor and Workforce Development Agency during the coronavirus pandemic when unprecedented numbers of people applying for unemployment benefits faced long wait times and the state paid out billions of dollars in fraudulent claims.

Industry groups have launched billboard and digital ads against Su in West Virginia, Montana and Arizona, while unions have assembled to support Su.

Sen. Bernie Sanders, the committee’s chair, voiced support as he opened Thursday’s hearing, saying the debate over Su “has nothing to do with her qualifications.”

“This debate really has everything to do with the fact that Julie Su is a champion of the working class of this country who will stand up against the forces of corporate greed,” he said.

But Democratic Sens. Joe Manchin, Jon Tester and Mark Kelly and Sen. Kyrsten Sinema, an independent, all declined to say whether they would vote for her confirmation this week. Democrats cannot afford to lose more than a couple votes in a Senate divided 51-49. Sen. Dianne Feinstein, D-Calif., is also recovering from shingles in California, with no firm return date.

Manchin repeatedly declined to comment on Su’s nomination this week; Tester said he would meet with her after the meeting to “make sure she’s still right”; Kelly said he didn’t have concerns about her record but added he does not preview his votes; Sinema said through a spokeswoman that she does not preview votes.

Su was confirmed by the Senate to her current role in 2021 by a 50–47 vote.

During her testimony, Su repeatedly referenced her work alongside Walsh, saying that Biden had asked her to “finish the job that Secretary Walsh and I started.”

Republicans appear unified in opposition to Su’s confirmation. Senate GOP leader Mitch McConnell of Kentucky said in a floor speech that Su “has a lengthy track record for all the wrong reasons.”

During the committee hearing, Republican senators closely questioned Su on whether she could forge relationships with industry groups, as well as her oversight of the California labor department when it paid out unemployment benefits to fraudulent claims during the pandemic.

The top Republican on the panel, Sen. Bill Cassidy, accused Su of unfairly favoring unions, telling her, “We need a labor secretary who is fair and unbiased in enforcing the nation’s labor laws.”

Su maintained a smile as she responded to Republican questions and emphasized that she knew the value of small business entrepreneurship through her parents. She insisted that she could build relationships with both labor and industry groups to help negotiate settlements and pointed out that Congress had lifted normal checks on unemployment claims for the enhanced benefits paid during the pandemic.

Late last year, Su was central to negotiations between labor and freight rail companies and helped avoid an economically debilitating strike. She has also led efforts to crack down on wage theft.

Republicans also asked if she would advance a California standard that classifies many workers as employees rather than independent contractors.

Su said she wouldn’t and understands the value of independent contractors. But she also asserted that “it is a problem in our economy that needs to be addressed” when businesses avoid paying minimum wage, overtime or unemployment insurance by classifying regular workers as independent contractors instead of actual employees.

The Senate committee is expected to vote next week on whether to advance Su’s confirmation to a vote in the full chamber.