A three-judge panel of the Ninth U.S. Circuit Court of Appeals may have been on solid legal ground when they agreed that school officials in Morgan Hill, Calif., could bar students from wearing U.S. flag T-shirts on Cinco de Mayo to prevent ethnic violence from students of Mexican ancestry, but their decision raises troubling concerns about threatening such violence as a means of suppressing free expression.

A 1969 Supreme Court case, Tinker v. Des Moines Independent Community School District, affirmed school officials’ authority to restrict the free expression of students if that expression would cause “material and substantial disruption of school activities or invasion of the rights of other students.” Thursday’s opinion by Judge M. Margaret McKeown, a Clinton nominee, notes that officials at Live Oak High School had reasonable fear of such disruption.