Gagne said the main issue comes to the health and safety of workers.
Local 710's Secretary Treasurer Wycliffe Oduor said it's not clear how long the most recent action, that began at 8 a.m., will last in Calgary.
"We don't want to shut down the postal service completely but we do want to make an impact on the employer - they're not being very forthcoming at the bargaining table", said Jarema.
Cheeke said over the past two years, workers have seen a 50 per cent increase in parcel delivery thanks to the rise of online shopping.
"More work, more parcels [and] forced overtime."
Postal workers in more than 20 communities across the country, including Calgary, Lethbridge and Medicine Hat were also on strike as negotiations between Canada Post and its workers remain stalled. Since the rotating strikes began on October 22, Canada Post reports operations in more than 70 communities across the country have been shut down. Marie, in Carbonear, Exploits Valley, Gander-Lewisporte, Deer Lake, St. Anthony and Stephenville, N.L., and in Bois-Francs region, Que.
Postal workers in Barrie hit the picket lines on Monday as the Canada Post rotating strikes across Canada continue.
The union and the postal service have been unable to reach new collective agreements for two bargaining units after 10 months of negotiations.
"As a result, customers could see delays of several days", Canada Post says in a release.
Last week, Labour Minister Patty Hajdu appointed Morton Mitchnick, a former chair of the Ontario Labour Relations Board, to help the two sides resolve their differences.