In a blow to labor interests, California Gov. Gavin Newsom vetoed a bill Friday that would have essentially prohibited self-driving trucks from traveling on the state’s public roads.

Assembly Bill 316 would have mandated autonomous trucks carry a human backup driver behind the wheel, a stipulation that autonomous-vehicle executives bemoaned would negate the purpose of deploying self-driving technology.

The bill was “unnecessary for the regulation and oversight” of self-driving trucks, Newsom, a Democrat, wrote to members of the California Assembly in explaining his decision.

Until Friday, AB 316 had gained considerable momentum. It passed the state’s assembly by a 69-4 vote in May and the state senate by a 36-2 vote earlier this month.

The International Brotherhood of Teamsters, which views autonomous trucking as a threat to union jobs, was a prominent backer of the bill.

But even as government leaders of all stripes seek to curry favor with union workers — see this week’s scheduled visits to UAW picket lines from President Biden and former President Donald Trump as prime examples — Newsom sided with Big Tech, another powerful constituency.

His veto did not go unnoticed from the Teamsters leadership.

“Gavin Newsom doesn’t have the guts to face working people,” Teamsters General President Sean M. O’Brien wrote in a Tweet. “Any politician who turns their back on workers to curry campaign contributions from Corporate America and Big Tech better square up.

“Teamsters will not walk away from this fight.”

The legislature could overturn Newsom’s veto with a two-thirds majority in each house, but it is unclear whether there’s appetite for such reconsideration.

Many self-driving trucking companies, including Kodiak Robotics, TuSimple, Aurora and Gatik, call California home. They say their technology can help with human-driver shortages and make port operations in places such as Oakland, Long Beach and Los Angeles more efficient.

“We commend Governor Newsom for vetoing AB 316,” said Jeff Farrah, executive director of the Autonomous Vehicle Industry Association. “As a result, California’s safety experts can continue to evaluate autonomous vehicle technology.”

The veto does not mean self-driving big rigs are free to roll.

The state currently prohibits the testing of autonomous-driving systems in vehicles that weigh more than 10,001 pounds. Companies have tested their self-driving trucks in places with industry-friendly regulations and laws — Texas has become a hotbed of self-driving truck activity.

AB 316 would have made California’s prohibition permanent.

Instead, Newsom indicated the California Department of Motor Vehicles will continue to examine its current regulations. The DMV held two public workshops regarding autonomous trucking this year, considered the start of a rule-making process.

The veto marked the second narrow victory for the self-driving vehicle industry in California this year.

The state’s Public Utilities Commission voted 3-1 in August to allow more extensive robotaxi deployments in San Francisco. That vote came despite concerns that vehicles are interfering with first responders in emergency situations and blocking traffic when they experience glitches.