MONTREAL -- A union representing dock workers at the Port of Montreal says it will launch an indefinite strike without an end date starting Monday.

The move expands the pair of four-day strikes by the Canadian Union of Public Employees that have diverted several ships to ports in Halifax, New York City and Saint John, N.B.

The announcement by CUPE follows escalating tensions between the union and the Maritime Employers Association amid a labour action revolving around wages and scheduling.

On Monday, the employer association informed the union it would cut overtime rates for work during evenings, weekends and nights, as the number of those shifts had increased due to daytime strikes.

Last week, police launched an investigation into a confrontation between dockworkers and port managers that erupted in violence at a parking lot where executives were exiting a shuttle bus.

The association says its preferred option remains negotiation and that it has submitted a "counter-proposal for a truce," but that the union's executive committee rejected it.

This report by The Canadian Press was first published Aug. 7, 2020.