Around 55,000 postal workers are now on strike.
The Canadian Union of Postal Workers says a strike came down to a last resort after a year of bargaining.
The strike comes ahead of Black Friday and the holiday season right when Canadians rely heavily on postal services to send and receive gifts.
Mail and parcels will not be processed or delivered during the strike with some post offices closed.
Service guarantees will be affected for items already in the postal network with no new items being accepted.
Federal Labour Minister Steven MacKinnon says federal mediators has been working with the union and crown corporation with a special mediator being appointed to support both sides.