Just over a year ago, the White House suffered an embarrassing defeat when three Democratic senators voted against advancing President Biden’s pick to run a key labor agency, dealing a blow to the administration’s pro-labor agenda.
On Thursday, the administration and Senate Democrats tried to ensure that history wouldn’t repeat itself, only this time the stakes were even higher.
The occasion was the Senate confirmation hearing of Julie Su, who has served as acting labor secretary since March 11 and is Mr. Biden’s choice to fill the job permanently.
As with last year’s confirmation battle, over the government’s top enforcer of minimum wage and overtime laws, Ms. Su’s nomination represents a broader fight over workplace regulation, with business groups chafing against Mr. Biden’s push to strengthen unions and increase workers’ rights and benefits.
And once again, there are signs that the administration may fall short, with at least two Democrats and an independent wavering over whether to support Ms. Su. A vote of the Senate Committee on Health, Education, Labor and Pensions is scheduled for next week.
In her testimony before the committee on Thursday, Ms. Su largely associated herself with the record of her predecessor, Martin J. Walsh — whom some Republicans and business groups have held up as pragmatic, and whom Ms. Su served as deputy.
She said she would seek employers’ advice on improving worker safety, and described the reverence she gained for small business owners after watching her immigrant parents operate a dry cleaner and a pizza franchise.
Democrats argue that Ms. Su, who has strong backing from labor unions, would be a strong worker advocate and enforcer of provisions like the minimum wage, safety regulations and restrictions on child labor, as well as the right to join unions.
“You need in terms of a bully pulpit a secretary of labor who makes clear that she is going to stand with working families, and she is prepared to use the powers of the office to take on corporate interests,” Senator Bernie Sanders, the Vermont independent who heads the labor committee, said in an interview on Wednesday.
If confirmed, Ms. Su is also likely to lead the Biden administration’s effort to expand overtime pay for salaried workers. The administration is expected to propose a rule substantially raising the salary threshold — currently about $35,500 — below which most workers automatically qualify for overtime.
Those questioning the merits of Ms. Su’s nomination have cited her record as California labor secretary and her support for the state’s labor regulations to suggest that she is a threat to certain industries.
When Senator Bill Cassidy of Louisiana, the committee’s ranking Republican, pressed at the hearing for assurances that she wouldn’t pursue regulations that could harm the franchise business model, Ms. Su reminded him that her parents had been franchise owners and suggested that their businesses “were the reason my sister and I were able to go to college.”
The Flex Association, a trade group representing several prominent gig economy companies, has called attention to her support for a California measure that would have effectively classified gig workers as employees, requiring companies like Uber and DoorDash to pay them a minimum wage and overtime and to contribute to unemployment insurance. (The law was later scaled back through a ballot measure.)
The group circulated an email on Wednesday expressing concern that Ms. Su “does not appreciate” that classifying gig workers as employees could cause many to lose access to such work.
Some labor experts have disputed this claim, and a rule being finalized by the Labor Department on how to classify workers takes a different approach from the California measure. But Kristin Sharp, the Flex Association’s chief executive, said that the labor secretary would have discretion over how to carry out the new rule and that “we want to make sure that person is objective in his or her views of nontraditional work.” The group has not taken an official stand on Ms. Su’s nomination.
Other business groups have cited what they say is Ms. Su’s support for a California law setting up a council to issue health and safety regulations for fast-food restaurants and create an industry-specific minimum wage.
“She has supported policies that directly attack our model,” said Matthew Haller, president of the International Franchise Association, alluding to the fast-food measure. A ballot measure next year will allow voters to decide whether to nullify the law. It is unclear from a video the groups point to that she has specifically supported the law.
And Republicans and a variety of business groups have highlighted accusations that California issued billions in fraudulent unemployment insurance claims while she was the state’s labor secretary in 2020. At the hearing, Mr. Cassidy recounted a report of a rapper securing hundreds of thousands of dollars in fraudulent funds in California and boasting about it on a video.
Ms. Su has conceded that a large number of claims were improper. Mr. Sanders pointed out that the overpayments reflected features of a federal program that the state merely administered, and that other states paid out a far higher percentage of fraudulent claims.
In recent weeks, a coalition of business groups has erected billboards and run ads critical of Ms. Su in the home states of potentially decisive senators, such as Joe Manchin of West Virginia, Kyrsten Sinema of Arizona and Jon Tester of Montana, all of whom have so far refrained from backing her nomination.
The effort is reminiscent of a business-backed campaign against David Weil, whom Mr. Biden tapped to head the Labor Department’s Wage and Hour Division in 2021, and who had led the agency during the Obama administration. That nomination died on the Senate floor last year after Mr. Manchin, Ms. Sinema and a third Democratic senator, Mark Kelly of Arizona, declined to support him. (Ms. Sinema has since become an independent.)
Mr. Weil and his backers lamented the muted response from progressive groups on his behalf. This time, labor unions and other supporters are making a more determined push. The A.F.L.-C.I.O. president, Liz Shuler, announced on Wednesday that a coalition of unions would make a “six-figure buy” of ads backing Ms. Su in states like Arizona and West Virginia and would urge local union members to contact their senators.
The United Mine Workers of America, which is influential in Mr. Manchin’s home state and sat out the fight over Mr. Weil, endorsed Ms. Su last week.
Emilie Simons, a spokeswoman for the president, said that the White House felt confident about Ms. Su’s confirmation and that it was working hard for every vote. She said that Ms. Su had offered to meet with every senator on the labor committee and that she had met with senators from both parties.
At a Senate Democratic lunch on Tuesday, Senator John Hickenlooper of Colorado, regarded as one of the more moderate Democrats on the labor committee, spoke up on Ms. Su’s behalf, noting her work on expanding apprenticeships as deputy secretary.
Mr. Hickenlooper said in an interview that he had watched Mr. Tester, his undecided colleague from Montana, as he delivered his remarks and that he was “hopeful that we’ll get him.”
But Mr. Manchin and Ms. Sinema may be harder to wrangle, according to veterans of such nomination fights. Mr. Manchin, who is up for re-election next year in a Republican-leaning state, has yet to meet with Ms. Su. Ms. Sinema is likely to face a challenge from a labor-backed candidate in her re-election bid, giving her little incentive to accommodate unions.
Larry Cohen, a former president of the Communications Workers of America who advises multiple unions and has helped secure the nomination of many pro-labor officials over the years, said that generating popular support for Ms. Su in Arizona and West Virginia might help her cause with Mr. Manchin and Ms. Sinema.
But, he added, “I think there is good reason to be worried about both of them.”
Jonathan Weisman contributed reporting.