Lakeland Union High School in Minocqua canceled classes Wednesday after concerning graffiti was found in a restroom.
The district says the message was reported to administration Tuesday afternoon at 3:35 p.m.
They say it was threatening, and included a drawing of a person holding a handgun.
Names of those potentially involved have been turned over to Minocqua Police, and those students will not be allowed to report to classes until they are cleared by the police department.
There is a reward for information leading to the arrest of the person or persons responsible.
Finals will go ahead at Lakeland Union High School today and tomorrow, with extra security precautions in place.