OTTAWA -- Vancouver and Niagara Falls, Ont., were added to the list of cities hit by postal disruptions this week as more Canadian Union of Postal Workers members walked off the job as part of rotating strikes.

About 3,400 CUPW members in Vancouver walked off the job early Friday, joining Canada Post employees in the Niagara and Sudbury regions of Ontario, and Saint John, N.B., who launched job action to back contract demands.

CUPW members have been conducting rotating walkouts across the country as a special mediator tries to bring the labour dispute to an end.

On 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.

Canada Post said it would work with the special mediator in hopes of reaching a negotiated settlement and indicated it would remain at the bargaining table.

"We remain committed to the bargaining process," Crown agency spokesman Jon Hamilton said in a statement.

Postal workers returned to their jobs late Thursday in Calgary and early Friday in Sherbrooke, Que., and Red Deer, Alta., after walking picket lines over a 24-hour period.

Nearly 9,000 CUPW members walked out for two days earlier this week in the Greater Toronto Area, creating delivery delays for tens of thousands of Canadians awaiting letters and parcels across the country. Postal workers in Kelowna, B.C., also joined the job action but have since returned to work.

"Our members would rather be doing their jobs than walking the picket line, but Canada Post has left us no choice," Mike Palecek, the union's national president, said in a statement.

"Canada Post needs to come to the bargaining table ready to talk about the issues that matter -- health and safety, equality for (rural and suburban mail carriers) and an end to precarious work."

CUPW and the postal service have been unable to reach new collective agreements for the two bargaining units in 10 months of negotiations.

Canada Post has made "significant offers" to CUPW -- which include increased wages, job security and improved benefits -- and has not asked for any concessions in return, Hamilton repeated Friday.

He said Canada Post is working to restore service and eliminate any mail and parcel backlogs.

"Canada Post continues to operate across the rest of Canada and is accepting and delivering mail and parcels in all other locations," Hamilton said.