Denise Mccrae is a school-board member in Mariposa County. Appalled by the amount of junk food in the schools, she convinces the state legislature to pass an ordinance that no stores may sell any unhealthy junk food within 600 feet of any school or daycare center. A political science teacher questions whether the regulation is valid and is told that it is a valid exercise of the jurisdiction's police power to protect its citizens. Convenience stores balk at the regulation and challenge it in court claiming that the law impermissibly affects interstate commerce. Restrictions on states' authority to pass laws that substantially affect interstate commerce are referenced by: