Police are investigating suspicious letter containing a powdery substance that was delivered to Calvin College.

According to an alert that was sent out to students, the school received a threatening letter in the mail print services building containing a powdery substance.

Police have closed the building, located at 3230 Lake Dr. SE on the north side of campus, as a precaution while they investigate the credibility of the threat.

Calvin College authorities say local and federal authorities are evaluating the credibility of this threat.