California will now require proof of vaccination or a negative Covid-19 test to attend large indoor gatherings of more than 1,000 people, according to a public memo released by state officials on Wednesday.

The state previously held these restrictions for large indoor gatherings of 5,000 people or more, but officials chose to create a stricter requirement due to rising cases of the Delta variant. The new restrictions will go into effect on September 20th, after which attendees to concerts, sports games, and other events of more than 1,000 people will be required to show proof of vaccination or negative Covid test results within 72 hours of the event. The testing requirement includes people who can’t yet receive the vaccine, such as children under 12.

Venues open to public circulation such as shopping malls, museums, and galleries are exempt from the rule unless they are hosting a qualifying event. Outdoor events are also exempt, although proof of vaccination or negative test is recommended, not required, for outdoor gatherings of more than 10,000 people.

The new vaccine requirements are slated to remain in place through November 1st, with officials deciding on an extension on October 15th.

California Governor Gavin Newsom initially announced the reopening of the state in June, lifting most Covid-19 restrictions, but several of those decisions have been reversed or revised in the wake of rising coronavirus cases. Masks are once again required indoors, even for vaccinated people, and statewide rules such as the indoor gathering restrictions are intended to encourage more residents to get the vaccine.