Brown issued a veto Sunday, saying "enabling illegal and destructive drug use will never work."
VIDEO: Here's what a safe injection site could look like in SF
San Francisco could still choose to open such a site but it would be in violation of federal and state law.
Advocates of "safe injection" sites say the supervised locations prevent drug overdoses and provide access to counseling.
RELATED: Safe injection sites remain hot debate in San Francisco
The U.S. government and other critics say taxpayers shouldn't be enabling users.
San Francisco Mayor London Breed has vowed to open a supervised injection site in the city, where public drug use is a major problem. She vowed to continue to work toward a solution and move the effort forward.
Despite the veto of #AB186, we will still continue to work with our community partners on trying to come up with a solution to move this effort forward. Thank you to @Scott_Wiener and @SusanEggman for their leadership in pushing this through the Legislature.— London Breed (@LondonBreed) October 1, 2018
Full statement: pic.twitter.com/3lPwRqPr1i
There are safe injection sites in other countries, but none in the United States.