Unionized workers from Canada Post took to picket lines in Winnipeg through Thursday night and into Friday.
The city was the first site in Canada to experience the rotating strike, with Hamilton, Ont. set to be the next location, beginning late Friday.
About 1,500 workers were on strike in Winnipeg.
Workers have a number of concerns, including health and safety. They said that because of a new computer sorting system at Canada Post's depot, letter carriers are required to carry two bundles of mail on their arm, instead of one.
The union said that system has led to a 15 per cent increase in trips, falls and injuries because carriers can't see their feet.
"The way they're asking us to work now - under the new model - has resulted in a sharp escalation in the number of injuries our members are suffering," said Darren Steinhoff from the Canadian Union of Postal Workers.
"I think the members have been very frustrated at the failure, or the lack of effort by the employer to resolve the issues," said Steinhoff.
Canada Post said the new system has been used for a decade in the U.S. without problems.
Canada Post also said it needs to address labour costs, noting letter-mail business has fallen more than 17 per cent since 2006 because of digital communications.
In Winnipeg, some businesses and charities expressed concerns over the effects of a strike.
The Siloam Mission shelter said it receives 90 per cent of its donations via mail and expressed worries if a strike persists.
Some other Winnipeg residents, however, said a postal strike wouldn't affect them.
Harsh Dubey said he doesn't rely on the mail.
"My communication is by email, cellphone, online, so I really don't care," he said.
Canada Post, meanwhile, said if a strike continues, everyone will start to notice.
It's asking the union to shut down picket lines.
"We have a great offer on the table. We should be hammering that out rather than worrying which city is next for strike action," said John Hamilton, from Canada Post.
Postal workers in Winnipeg are slated to be back at work at 11 p.m. Friday, while the rotating strike is slated to move next to Hamilton.
Federal cheques, such as pensions, will still be delivered during a strike.
A list of depots where provincial cheques will be available for pick up is also available on the province's website.
The City of Winnipeg advised people to call 311 for information on how city services that normally use Canada Post will operate during the work stoppage. Bills will still be required on time, said city officials. More information is also available on the city's website.
- with a report from CTV's Jeremy Hunka
- with files from The Canadian Press
