The Diocese of Rockville Centre warned their three high schools on Long Island that students or fans kneeling or protesting during the national anthem before games or other school events could face​ “serious disciplinary action.”

​“This is a reminder that all student-athletes and spectators are expected to stand during the playing of the National Anthem at school sporting events, without any gestures of demonstration or protest,” ​the diocese wrote in the directive sent this week, Newsday reported.

It said the “long-standing school policy … applies equally to all participants and audiences at all school events, including those that are not sporting; for example, concerts and plays.​”​

The statement was sent to the three high schools in the diocese — ​St. John the Baptist in West Islip, Holy Trinity in Hicksville and McGann-Mercy in Riverhead.

​”We ask our students also to recognize that failure to abide by this policy may result in serious disciplinary action,” it said.

Discipline will be handled on a case-by-case basis, diocese spokesman Sean Dolan told Newsday.