The union representing workers at Canada's two main rail companies said on Friday it had filed court challenges against rulings by the country's industrial labor board that forced them back to work, Reuters reported. 

On Saturday, the board accepted a request from the government to order more than 9,000 Teamsters members back to work at Canadian National Railway CNR.TO and Canadian Pacific Kansas City and to impose binding arbitration.

The union had already said it would appeal the rulings on the grounds that they were a win for the railways and could lead to the imposition of future contracts, eroding workers' bargaining power.

"These decisions, if left unchallenged, set a dangerous precedent where a single politician can bust a union at will," said Paul Boucher, president of the Teamsters rail union.

"The right to collectively bargain is a constitutional guarantee. Without it, unions lose leverage to negotiate better wages and safer working conditions for all Canadians," he said in a statement. The union filed the challenges in the Federal Court of Appeal and asked that the proceedings be expedited. However Canada's justice system is famously slow-moving and whoever loses the appeal is likely to take it to the Supreme Court, which means the case could take years to resolve.

There was no immediate reaction from either rail company or from federal Labour Minister Steven MacKinnon. He has already said he is confident his decision to refer the matter to the board would survive a court challenge given his broad power under Canada's labour code.

Government officials say the challenge is separate from the board's ruling and will not affect the return to work.

The two companies locked out the workers earlier this month after talks failed to produce a new labor deal.