A southern Illinois school district is weighing its options after an activist group has threatened to sue if prayers offered at graduation ceremonies aren’t halted.

The American Humanist Association’s legal arm has sent letters warning of the potential lawsuit to Norris City-Omaha-Enfield High School administrators. The group insists that by including prayers during the high school’s graduation ceremony, the district unconstitutionally coerces students to participate in a religious activity.

The high school’s principal, Matt Vollmann, says the student-led prayer long has been part of the ceremony, and that he’s never fielded any local complaint.