SACRAMENTO, Calif. (AP) — California is changing its standards for when police can kill under a law signed Monday by Gov. Gavin Newsom, as it tries to deter police shootings of young minority men that have roiled the nation.

“We are doing something today that stretches the boundary of possibility and sends a message to people all across this country that they can do more and they can do better to meet this moment,” Newsom said as he stood alongside family members of people killed by police.

The law by Democratic Assemblywoman Shirley Weber of San Diego will allow police to use lethal force only when necessary to defend against an imminent threat of death or serious injury to officers or bystanders. But lawmakers dropped an explicit definition of “necessary” that previously had said officers could use deadly force only when there is “no reasonable alternative.”

One catalyst was last year’s fatal shooting of Stephon Clark, an unarmed black man suspected of vandalism whose death sparked major protests in the state capital and reverberated nationwide. Despite the public anger, law enforcement objections stalled the bill last year and even some supporters had reservations until it was amended in May.

The measure passed with bipartisan support after major police organizations won concessions and ended their vehement opposition.

Lawmakers also removed an explicit requirement that officers try to de-escalate confrontations. Law enforcement officials said that would have opened officers to endless second-guessing of what often are split-second life-and-death decisions.

The measure still contains the strongest language of any state, according to the American Civil Liberties Union, which proposed the bill and negotiated the changes.

Weber said the law “changes the culture of policing in California.” She was joined on stage by fellow lawmakers and family members of people who have been shot by police, including Clark’s family and the mother of Oscar Grant, a man killed by police officers on an Oakland train platform in 2009.

It is linked to a pending Senate bill requiring that officers be trained in ways to de-escalate confrontations, alternatives to opening fire and how to interact with people with mental illness or other issues.