The legislation vetoed Friday night would have banned self-driving trucks weighing more than 10,000 pounds (4,536 kilograms) — ranging from UPS delivery vans to massive big rigs — from operating on public roads unless a human driver is on board.

Lorena Gonzalez Fletcher, head of the California Labor Federation, said driverless trucks are dangerous and called Newsom’s veto shocking. She estimates that removing drivers would cost a quarter million jobs in the state.

“We will not sit by as bureaucrats side with tech companies, trading our safety and jobs for increased corporate profits. We will continue to fight to make sure that robots do not replace human drivers and that technology is not used to destroy good jobs,” Fletcher said in a statement late Friday.

In a statement announcing that he would not sign the bill, the Democratic governor said additional regulation of autonomous trucks was unnecessary because existing laws are sufficient.

Newsom pointed to 2012 legislation that allows the state Department of Motor Vehicles to work with the California Highway Patrol, the National Highway Traffic Safety Administration “and others with relevant expertise to determine the regulations necessary for the safe operation of autonomous vehicles on public roads.”

Opponents of the bill argued self-driving cars that are already on the roads haven’t caused many serious accidents compared to cars driven by people. Businesses say self-driving trucks would help them transport products more efficiently.

Union leaders and drivers said the bill would have helped address concerns about safety and losing truck driving jobs to automation in the future.

The bill coasted through the Legislature with few lawmakers voting against it. It’s part of ongoing debates about the potential risks of self-driving vehicles and how workforces adapt to a new era as companies deploy technologies to do work traditionally done by humans.

Newsom, who typically enjoys strong support from labor, faced some pressure from within his administration not to sign it. His administration’s Office of Business and Economic Development says it would push companies making self-driving technologies to move out-of-state.

The veto comes as the debate over the future of autonomous vehicles heats up. In San Francisco, two robotaxi companies got approval last month from state regulators to operate in the city at all hours.

Last Tuesday in Sacramento, hundreds of truck drivers, union leaders and other supporters of the bill rallied at the state Capitol. Drivers chanted “sign that bill” as semi-trucks lined a street in front of the Capitol. There are about 200,000 commercial truck drivers in California, according to Teamsters officials.