A group representing 150,000 truckers is calling on the US Senate to oppose President Joe Biden’s pick for Labor Secretary over a California labor rule it says has stifled drivers’ independence.

The Owner-Operator Independent Drivers Association asked a Senate panel to block the nomination of Deputy Labor Secretary Julie Su based on her backing of the 2019 California contract-worker law, known as AB5, in her previous role as the state’s labor secretary.

“The law and its haphazard rollout has forced independent contractor truckers to leave the state of California, become an employee, attempt to reconfigure their business, operate under a cloud of uncertainty, or abandon the trucking profession altogether,” OOIDA CEO Todd Spencer said in a March 3 letter to Senate Labor Committee Chairman Bernie Sanders and ranking member Bill Cassidy.

AB5’s aim is to improve working conditions for contractors including tens of thousands of independent drivers in California, though opponents say it’s upending the industry. It requires workers to satisfy a three-part test to be considered independent contractors, or else be seen as employees entitled to job benefits. The trucking industry relies on contractors — who have valued the flexibility to operate on their own terms — and has fought to be exempt from state regulations for years.

The Labor Department’s office of public affairs didn’t respond to a request for comment. The letter was first reported by the Journal of Commerce. 

Many in the California logistics industry have complained of uncertainty and confusion over how to comply since the Supreme Court refused to review a case from the trucking industry challenging the law last summer.

The group said it’s especially concerned that Su will try to challenge policies similar to AB5 at the national level. “What happened in California is so overly broad,” Spencer said in an interview. “We don’t want a repeat of that in D.C.”

Last week, Biden announced his intent to nominate Su to replace outgoing Labor Secretary Marty Walsh. The position requires Senate approval.