The Canadian Union of Postal Workers says its rotating strikes have moved to the Outaouais.
Workers in that region hit the picket lines at 5:00 a.m. Thursday.
This comes after CUPW workers in Ottawa, Arnprior and Renfrew walked off the job Wednesday.
Workers in Ottawa remain on the picket lines Thursday morning. The strike ended in Renfrew and Arnprior at 7:00 a.m.
CUPW and the postal service have been unable to reach new collective agreements in 10 months of negotiations.
"We outlined our major issues to Canada Post at the very beginning of the negotiation process ... and clearly stated that we would not sign any agreements that don't address overwork and overburdening, equality and full-time jobs," CUPW national president Mike Palecek said in a statement earlier this week.
"Our position hasn't changed. We aren't just bargaining for today, we are bargaining for the future -- for our members and everyone who relies on the postal service."
Last Tuesday, Labour Minister Patty Hajdu appointed Morton Mitchnick, a former chair of the Ontario Labour Relations Board, to help the two parties resolve their contract differences.
New Thursday, Canada Post says they're dealing with a significant parcel backlog -- 150 trailers filled with packages that still need to be processed and delivered are sitting in Toronto, Vancouver, and Montreal.
But CUPW has announced an overtime ban for its workers who aren't on strike, meaning those workers are to refuse working more than 8 hours in a day and 40 hours in a week.
With files from The Canadian Press.