Huntington, W.Va. (AP) — A West Virginia school superintendent is investigating a Feb. 2 religious revival event that occurred at Huntington High School, saying he believes some students’ rights have been violated.

Cabell County Schools Superintendent Ryan Saxe announced the investigation in a statement issued Friday. About 100 students at the high school walked out in protest Wednesday during an advisory period, chanting, “Separate the church and state” and, “My faith, my choice.”

The Fellowship of Christian Athletes had invited Nik Walker Ministries to hold a revival at the school, which was advertised as a voluntary event. School officials have said there was supposed to be a sign-up sheet to attend but that two teachers mistakenly took their entire classes.

That prompted complaints from some parents and from students who organized the walkout.

“It was reported to my staff that some students were required to attend a religious event during the school day,” Saxe said in the statement. “At this point in the investigation, it is my belief that some students’ rights have been violated. As the investigation continues, we must follow due process, which takes some time, in addressing any responsible employee while working to ensure a situation like this never occurs again.”

Saxe said the district honors students’ rights to express their views and respects their right to religious expression but that “forcing religious expression on those with differing beliefs is not acceptable and is not in alignment with district, state, or federal policy and will not be tolerated by my administration or the Board of Education.”