Jean-Pierre Fortin, president of the Customs and Immigration Union, says the guards were asked a few months ago to provide backup for the RCMP less than a kilometre away from the Canada-U.S. border in Emerson.
He says the guards left their posts to help the Mounties, who were staking out a kidnapping suspect at a nearby bar.
Fortin says the border remained staffed by other guards on shift and the three guards returned to their posts less than an hour later following the arrest.
He says the Canada Border Services Agency investigated and has suspended the guards for up to 25 days without pay because they left their posts for an "unauthorized purpose."
Fortin says the guards were compelled by the Criminal Code to help the RCMP and should be commended rather than punished.