The new rule from the California Department of Public Health takes effect starting Sept. 20.
It includes several changes from state vaccine rules for indoor events that had been put in place previously.
Under the previous rules, people were allowed to self-attest to their vaccination or negative test status. Now they will be required to show proof.
In addition, the threshold for indoor events for the rules to apply was lowered from 5,000 people to 1,000.
"The Delta variant has proven to be highly transmissible, making it easier to spread in large crowds where people are near each other for long periods of time," said Dr. Tomás J. Aragón, CDPH Director and State Public Health Officer. "By requiring individuals to be vaccinated, or test negative for COVID-19 at large events, we are decreasing the risk of infection, hospitalization and death."