The Canada Industrial Relations Board says Air Canada flight attendants can't legally strike after Labour Minister Lisa Raitt referred the negotiations between the airline and the union to the board.

The Canadian Union of Public Employees, which represents about 6,800 Air Canada flight attendants, had planned to strike at 12:01 a.m. Thursday.

Raitt sent two referrals to the quasi-judicial board at about 2 p.m. Wednesday.

Under the Canada Labour Code, the CIRB can issue an order that will prevent a work stoppage so that it does not "threaten public safety or health."

"Our government received a strong mandate to protect the Canadian economy and Canadian jobs, so we have been closely following the negotiations between Air Canada and CUPE," Raitt said in a statement Wednesday afternoon.

Saying that a negotiated agreement is unlikely to occur in the near future between the two sides, Raitt asked the CIRB to consider imposing an agreement upon the two parties, or to send them to binding arbitration.

Both sides must continue normal working activities while the CIRB, an independent tribunal, makes a decision.

Prior to Raitt's announcement, Air Canada's flight attendants said they were still planning to walk off the job at midnight despite indications that the federal government planned to block the labour action.

CUPE announced on Sunday that nearly two-thirds of the flight attendants who took part in a vote did not support a deal that had been negotiated with Air Canada.

That put the flight attendants in a legal strike position.

Air Canada has said it is preparing for the likely possibility that its 6,800 flight attendants could be headed off the job.

The flight attendants rejected a prior tentative agreement in August, which sent union negotiators into a new set of talks with the airline. Air Canada produced a deal that was turned down Sunday.

Some of the key issues in the dispute between the flight attendants and the airline include wages, pensions, crew rest, working conditions and work rules.

Raitt said Tuesday that union officials told her they had received 80 per cent of what they asked for, so it is unclear "what the difficulty is."

"In this case, we've got a situation where two times you've had unanimous recommendation of a deal and two times ratification has failed," Raitt told CTV Power Play. "We want to know why, what happened, and we want the parties to talk about what their process was, and maybe there's something that happened within the ratification vote that the CIRB can take a look at."