OTTAWA (Reuters) - The union representing workers at Canada's two main rail companies said on Friday it had filed four court challenges against a ruling by the country's industrial labor board that forced them back to work.

The board on Saturday accepted a request from the government to order more than 9,000 Teamsters members back to work at Canadian National Railway ( CNI ) and Canadian Pacific Kansas City ( CP ) and to impose binding arbitration.

The union said the decision was a win for the railways and could lead to the imposition of future contracts, eroding workers' bargaining power.

Federal Labour Minister Steven MacKinnon said last week his decision to refer the matter to the board would survive a court challenge given his broad power under Canada's labor code.

Government officials say the challenge in the Federal Court 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.

(This story has been refiled to remove an extraneous work in paragraph 1)