Dockworkers at the Port of Montreal walked off the job early Sunday for a one-day strike aimed at putting pressure on their employer amid difficult contract talks.

The union representing nearly 1,200 longshore workers at the country’s second biggest port served notice Thursday for a complete work stoppage from 7 a.m. Sunday until Monday morning.

The move comes on top of an ongoing strike on overtime shifts and a three-day strike at two container terminals that ended earlier this month.

The Maritime Employers Association says the work stoppage includes the Montreal port and the Contrecoeur terminal, but activities related to grain vessels and the supply of Newfoundland and Labrador will be maintained in line with a July decision of the Canadian Industrial Relations Board.

“The MEA hopes that upcoming discussions with the Federal Mediation and Conciliation Service will be fruitful and will lead to a return to the negotiation table to quickly reach a negotiated collective agreement,” the company wrote in a news release on Saturday.

It said last week that the parties remain at an impasse after 35 mediation meetings over 15 months.

A spokesperson for the union said the striking workers were holding a special general assembly Sunday morning but did not release details of the agenda and did not make anyone available for an interview.

The Canadian Federation of Independent Businesses said in a statement that the union’s actions are affecting small and medium-sized businesses, especially ahead of the busy holiday shopping season.

“It’s time the federal government made ports an essential service so that they remain operational at all times,” wrote Jasmin Guenette, the federation’s national affairs vice-president.

The workers have been without a collective agreement since Dec. 31, 2023.