OTTAWA -- The union representing Canada Post employees says workers in five Ontario southern communities have walked off the job as rotating strikes across the country enter the third week.

The Canadian Union of Postal Workers says the workers in Amherstburg, Delhi, Owen Sound, Sarnia and St. Thomas began striking just after midnight today.

CUPW says employees in Newfoundland and the Ontario communities of Brantford, Fort Erie, Guelph, Simcoe, St. Catharines and Welland returned to work early this morning after striking for 24 hours.

The union says it has called on a national overtime ban for both of its major bargaining units at Canada Post, meaning postal workers will not work more than an eight-hour day and no more than a 40-hour week.

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

Canada Post has said that the rotating strikes have affected operations in more than 70 communities across the country, causing backlogs that could delay mail delivery to its customers for several days.