Montreal's international theatre festival has been forced to cancel its opening show due to a union dispute, leaving organizers scrambling to find a replacement show.

The Festival TransAmériques​ had invited Toronto's Canadian Stage theatre company to perform a multi-media piece called Helen Lawrence next month.

Marie-Helene Falcon, the artistic director of the theatre festival, said she was looking forward to opening with a Canadian production for the first time.

"It's so sad, it's really an awful situation," said Falcon. "It would have a great moment, and all this is lost."

Helen Lawrence is the creation of Vancouver photographer, Stan Douglas, and TV writer, Chris Haddock, the screenwriter of Da Vinci's Inquest.

The show was called off Tuesday because of a dispute between Canadian Actors Equity Association and the theatre company.

The issue is Equity's stipulation that there be an eight-week break between productions or the theatre company pay the actors during that break.

Usually in a scheduling conflict like this, the union and the theatre company make a concession to allow the performance to go ahead.

"It's a very difficult scenario and that's why there's a provision for the concession to be agreed to, but Equity felt it was not in their best interest to agree," said Su Hutchinson, the manager of Canadian Stage.

Equity President Arden Ryshpan issued a statement saying that Canadian Stage requested the concession "only after the Helen Lawrence engagement was already underway," and suggested the theatre company should have put some money on the table.

The theatre company maintains it followed proper procedures.

People who have tickets can either get reimbursed or exchange them for another production at the festival.

The opening performance is scheduled for May 22.