Margaret Murphy, a spokeswoman for the Halifax university, says Mitch Hannigan retweeted an image that purportedly shows an American female beach volleyball player with the words, "Give your cheeks a pinch" below her buttocks.
Murphy says the university believes the retweet is intended to be a fake or joke ad.
She says in retweeting the image, Hannigan didn't meet standards set out an agreement the school has all coaches sign.
The agreement says coaches of club teams will behave in a way that promotes "the highest principles, integrity and dignity of the sport."
Hannigan didn't respond to an emailed request for comment.
The campus introduced education programs for athletes on respectful behaviour after a video surfaced in the fall of last year showing student leaders singing a chant about underage, non-consensual sex during orientation week.