OTTAWA – The union that represents Canada Post workers is filing a constitutional challenge over the federal government’s back-to-work legislation.

The Canadian Union of Postal Workers (CUPW) says they will be filing the challenge with the Ontario Superior Court.

“This law violates our right to free collective bargaining under the Charter of Rights and Freedoms,” said Mike Palecek, CUPW National President in a statement on Tuesday.

The union had said “all options” were on the table after Labour Minister Patty Hajdu tabled, and passed Bill C-89, forcing striking workers back on the job in late November, under the existing collective agreements while continuing contract negotiations.

Yesterday, Hajdu appointed a new mediator-arbitrator after Canada Post and CUPW were unable to agree on a suitable person to bring to the table to help the two parties negotiate new collective agreements. The new mediator has the ability to impose a settlement through binding arbitration.

The constitutional lawyer representing the union said that Canada Post “created a false emergency,” of a package backlog to compel the government to intervene with the back-to-work bill.

“This legislation was enacted under circumstances that did not justify the interference of constitutional rights,” lawyer Paul Cavalluzzo said in the statement.

Bill C-89, the “Postal Services Resumption and Continuation Act," passed on an accelerated and dramatic timeline that included the Senate sitting over a weekend; Hajdu being met with chants of “Shame! Shame!” from the public viewing galleries where postal workers had convened; and NDP MPs staging a walkout in solidarity with the workers.

The union claims that, under the existing agreements, more postal workers will be injured on the job, and rural and suburban mail carriers will continue to work unpaid overtime.

The last time back-to-work legislation was used for Canada Post workers was by the then-Conservative government in 2011. It was also challenged in court and, five years later, found to be unconstitutional.

Hajdu has defended this new bill as taking a different, more "fair and balanced" approach, and said it was not a step they took lightly.

“Obviously we can’t comment on matters that are before the court,” Hajdu said when asked about the challenge today on Parliament Hill. “The courts will take their time... But as far as we’re concerned the mediator-arbitrator has important work to do.”