The arbitrator appointed by the government to negotiate a new contract between Canada Post and its union has stepped down.

Labour Minister Lisa Raitt appointed Judge Coulter Arthur Anthony Osborne as the arbitrator in the case following controversial back-to-work legislation.

The Canadian Union of Postal Workers challenged Osborne because he is unilingual and doesn’t have a labour relations background.

Last month, the union won a stay of proceedings in the arbitration. The Federal Court ruling meant they couldn’t start the arbitration until after the court heard the union’s case against Osborne in January 2012.

The union is asking to meet with Raitt to discuss the next appointment.

Dénis Lemelin, head of CUPW, says the union got a letter Wednesday night from Osborne saying that he was resigning.

"We wrote a letter to the minister this morning asking for a meeting with her, suggesting that she find a way that we go back to the table," he said.

"We want to meet with her to explain our position and we want to suggest that the best way to address the issue is really to have someone like an experienced and bilingual mediator that can ... try to force the party to negotiate a collective agreement," Lemelin added.

"The best way is to really have a negotiation."

A spokeswoman for Raitt said in a statement that all Canadians need the matter settled.

"The law clearly states that the parties can always seek to negotiate their own deal," and Raitt encourages them to do so, Ashley Kelehear wrote in an email.