Customs agents who work at Trudeau International Airport protested during their lunch hour on Thursday.
Dozens of employees held picket signs as they marched around the International Arrivals section of the airport.
They say they are concerned about how cuts to manpower, and the replacement of border agents with machines, will affect national security.
Jean-Pierre Fortin, the national president of the Customs and Immigrations Unions, said reducing the number of agents will make it more likely that individuals who are normally turned away will be permitted into the country.
"People will be cleared, talking on a phone to a person out in Ontario, in Hamilton to be precise, and he will make the determination if this person should be coming in this country. It's not acceptable," said Fortin.
Union members say they also anticipate there will be fewer seizures of drugs, counterfeit money and other items.
The federal government introduced Automated Border Clearance machines at three airports in Canada in 2013, and border agents say depending on a machine to replace a human will be dangerous.
Border agents have been without a contract since 2011.
