Nearly all of the Six Flags parks in the U.S. have announced a new policy limiting the size of bags that guests can bring into the park.

In a series of social media posts Friday, parks across the chain announced, “For the duration of Fright Fest, Six Flags has implemented enhanced public safety measures, including x-ray screening of all bags and limiting bag size. Bags, including backpacks and purses, must be no larger than 12 inches by 12 inches by 6 inches to enter the park.”

Policies on individual Six Flags websites clarify that, “Exceptions will be made for bags carried for medical reasons and diaper bags that accompany infants and young children.”

The only Six Flags parks that have not announced such a policy change are Frontier City in Oklahoma City and Six Flags Great Escape in Queensbury, New York.

Limiting bag sizes and increasing security has been commonplace in the theme park industry in recent months due to violent incidents involving guests, most recently a shooting at Kennywood in Pittsburgh. Six Flags has not been immune, with a drive-by shooting occurring in Six Flags Great America’s parking lot earlier this year and fights at Six Flags America forcing the park to shut down early last September.