OTTAWA, Aug 30 (Reuters) - 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.

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 ( CNI ) and Canadian Pacific

Kansas City ( CP ) 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 labor 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.