A union representing workers on the Canadian side of the St Lawrence Seaway are threatening to strike if they fail to reach an agreement by Saturday night.

If the strike goes forward, it would shut down locks that connect the Great Lakes to the Atlantic for tankers, bulkers and other ships that use the waterway. All but two of the 15 locks are managed by Canada’s St Lawrence Seaway Management Corp.

Unifor, the union representing its workers and issuing a 72-hour strike notice on Wednesday, said on Friday that it is willing to continue negotiations even after scheduled bargaining dates have passed.

Lana Payne, the union’s national president, said Unifor is committed to a collective agreement.

“But at this moment, the employer is not,” she said. “We are staring down a strike deadline, and it’s time for St. Lawrence Seaway to get serious.”

The negotiations have continued for months for workers in the provinces of Quebec and Ontario.

St Lawrence Seaway Management, a nonprofit corporation set up by the Canadian government, said it is also committed to the negotiation process.

But the outfit said that for a not-for-profit organisation, the union’s high wage demands could require tolls to rise to a level that is not competitive and could increase prices for goods travelling on the waterway.

The company is preparing for an orderly shutdown, with 80 vessels in the seaway on Friday, including 40 oceangoing ships.

“Any shutdown, even a short one, will negatively impact the seaway as we enter into the busy part of the navigation season,” the outfit said.