The union representing more than 9,000 workers at Canada’s two largest railways filed a legal challenge of the decisions that suspended their right to strike and sent them back to work.

Canadian National Railway Co. and Canadian Pacific Kansas City Ltd. locked out employees on Aug. 22 after contract talks with the Teamsters Canada Rail Conference failed. Less than 17 hours later, Labor Minister Steven MacKinnon stepped in, asking an independent labor tribunal to order arbitration to settle the dispute and telling the railways to resume operations.

Canadian Pacific’s unionized employees then went on strike and Canadian National’s workers announced they would begin a strike Aug. 26. But the tribunal, the Canada Industrial Relations Board, sided with the minister on Aug. 24, forcing CP’s workers back and preventing a CN strike before it could begin.

The Teamsters’ appeals, filed with the Federal Court of Appeal, argue that workers’ rights were violated and that the minister’s request and the CIRB’s order were unconstitutional.

“These decisions, if left unchallenged, set a dangerous precedent where a single politician can bust a union at will,” Paul Boucher, president of the Teamsters Canada Rail Conference, said Friday in an emailed statement. 

“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. We are confident that the law is on our side, and that workers will have their voices heard.”