The union representing tugboat crews in ports across B.C. says members will hold a strike vote Tuesday as Seaspan threatens to impose changes to a collective agreement.

Terry Engler, president of the International Longshore and Warehouse union, Local 400, says the company is set to make 46 changes to the contract next week.

He says the local has not been on strike since it was formed in the 1950s and any job action resulting from what he calls Seaspan's confrontational approach could cripple operations at Port Metro Vancouver, Deltaport and other ports.

Story continues below advertisement

Engler says Seaspan tugs do most of the work on the waterfront, assisting freighters, tankers and other vessels docking and leaving port.

Captain Mike Armstrong, president of the western branch of the Canadian Merchant Service Guild, which represents tugboat captains and engineers, says Seaspan is also threatening to unilaterally impose contract changes on its members.

Armstrong's union will take a strike vote Wednesday against the company that provides marine transportation.