The Canadian Union of Postal Workers rejected the Crown corporation's latest offer and is now asking for the federal government to appoint a mediator in its contract talks with Canada Post.
The Prime Minister issued a last-minute plea to both sides before the midnight deadline.
In a Twitter post, Justin Trudeau called on them ``to resolve their differences quickly and reach a deal" with the arrival of the holiday shopping season.
But as the deadline passed, CUPW issued a statement saying it had responded ``by presenting the Corporation with our own global offers that address our needs and demands.''
It also asked for a mediator to help the two sides reach an accord after nearly a year of talks.
CUPW had said on Friday that the new proposals from Canada Post made positive steps, but not enough to end the rotating strikes that have shut down postal operations in more than 200 communities, creating a huge backlog of undelivered mail. It said it would not bring the offers to a vote of its members, although both sides remained at the bargaining table.