Postal workesr walk a picket line at the Canada Post facility in Kitchener, Ont., on Friday, June 10, 2011.
Postal union leaders have targeted Canada's two largest urban centres as their next strike targets.
The Canadian Union of Postal Workers says about 15,000 of its members will walk off the job in Toronto and Montreal at midnight.
The planned 24-hour walkout is the latest in a string of rotating work stoppages as the union attempts to put pressure on Canada Post to come to an agreement in their contract dispute.
The union representing some 50,000 urban postal workers began the rotating strike almost two weeks ago.
Some 10 locations from Corner Brook, Nfld., to Nanaimo, B.C., were hit on Monday.