The 600 employees work for the security company Securitas. This marks the second time workers with the Metallos union have turned down an offer in three months.
Michel Courcy, the head of the union, said talks broke down over the issue of salaries. The union said its members are effectively paid less than those who do the same work at the Quebec City and Toronto airports.
"We hope to negotiate and arrive at an agreement without having to disturb airport service. But if it's necessary, control agents are prepared to go on strike," Courcy said in a press release.
Since negotiations began in October, agents have been using pressure tactics including wearing camouflage pants, pajamas or union caps.
"Montreal agents will not accept being treated like second-class workers. Their work is essential for the safety of air transport. It's a job with great responsibility and their salaries should better reflect that." Courcy stated, adding that current Montreal wages range between $15 and $21 per hour.
The workers have been with out a contract since the end of October 2012.