St. Thomas Aquinas High School in Tottenham has been closed for the day.
The Simcoe Muskoka Catholic District School Board made the decision due to a possible threat.
Police arrived on the scene early this morning to conduct the investigation.
The school was placed in look down.
Father FX O'Reilly was also placed in a lock down temporarily as a precaution.
According to police, a shooting threat was made on social media last night (April 19).
The post did not specify which St. Thomas Aquinas so, Peel Regional Police locked down the Brampton location as well.
Police say all staff and students are safe and secure at both schools.