Unifor issues 72-hour strike notice for St. Lawrence Seaway workers.

Container ships are shown in the Port of Montreal on January 4, 2016. THE CANADIAN PRESS/Graham Hughes

Unifor says workers for the St. Lawrence Seaway could strike as early Sunday.

The union has issued a 72-hour notice to strike for five local units who represent 361 maritime workers in the seaway starting as soon as 12:01 a.m. on Sunday, Oct. 22.

Unifor says a strike would effectively shut down transit through the seaway.

"Employers have seen that workers will absolutely use their right to strike when they feel it’s necessary, and our members in all units at the Seaway have had enough," said Lana Payne, Unifor National President.

"It’s time to come to the table with a serious wage offer or the employer can watch what happens when workers stand together and demand their fair share."

A statement by the St. Lawrence Seaway Management Corporation (SLSMC) said they are committed to obtaining a fair settlement but a strike would have a severe impact on the North American supply chain.

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"This labour action would impact grain movements during a period when the world is in dire need of this essential commodity, even as supply has been affected by the situation in Ukraine and the greater frequency of extreme weather events being experienced around the world," a statement by SLSMC said.

The SLSMC said they are preparing detailed plans for a safe shutdown of the system should a strike be called.

"This employer has shown no willingness to address the workers' concerns in the workplace or approach them with a respectful wage offer," said Daniel Cloutier, Unifor Quebec Director.

"A strike is always a tool of last resort when it comes to negotiations, but these workers have been clear and are united in their goals – they’re ready."

Negotiations will continue today and over the weekend to reach a deal with the assistance of a federally-appointed mediator.