The union representing 6,800 Air Canada flight attendants says it has cancelled its planned strike for 12:01 a.m. Thursday, after the Canada Industrial Relations Board said employees must remain on the job while their contract dispute is being reviewed.

"Flight attendants represented by the Canadian Union of Public Employees (CUPE), will not be going on strike tonight, as previously planned, following a notice by the Canadian Industrial Relations Board," the union said in a statement issued Wednesday afternoon.

"The minister’s intervention with the labour board, as it stands, postpones the calling of a strike until the question of essential services has been ruled on."

The CIRB said in a statement earlier Wednesday that it is being asked by the federal government  to determine, under section 87.4 of the Canada Labour Code, "whether any services need to be maintained, in the event of a strike or lockout, to prevent an immediate and serious danger to the safety or health of the public.

"In this regard, the Code is clear that this referral suspends the right to strike or lockout until the board renders a decision on this matter," it said.

CUPE received formal notice Wednesday that Labour Minister Lisa Raitt had referred the contract dispute to the CIRB. 

Her referrals ask the tribunal to decide whether the union membership's rejection of two tentative deals has "created conditions that are unfavourable" to settling the dispute, whether communities might be cut off from service to urban centres and what effect that would have on Canadians' health and safety.

Earlier in the day, CUPE had insisted it was in a "legal strike position," while adding it remained available to resume negotiations with Air Canada.

In a statement Wednesday, Raitt said the Conservative government had been given a "strong mandate to protect the Canadian economy and Canadian jobs, so we have been closely following the negotiations between Air Canada and CUPE."

"I have asked the CIRB to review the situation at Air Canada to ensure that the health and safety of the public will not be impacted, and to determine how best to maintain and secure industrial peace and promote conditions that are favourable to the settlement of industrial disputes," the minister said.

But CUPE national president Paul Moist called Raitt's decision to go to the CIRB "outrageous."

"Her rationale for this is disingenuous, and the use of the Canada Labour Code and the CIRB in this way is indefensible," Moist said in a statement.

Later, Moist said Raitt is using tactics that have nothing to do with health and safety

"It's got to do with the fact that she's got legislation on the order paper, Parliament's not meeting this week, the government's not inclined to call government back and this government doesn't want strikes," Moist told CBC's Power & Politics with Evan Solomon.

CUPE spokesman Robert Lamoureux echoed the sentiment.

"It's something fundamental to us — the right to withhold labour if we cannot reach a settlement," Lamoureux said. "If we lose that right, employers will be able to have the upper hand in every situation."

Illegal strike

Labour lawyer Paul Cavalluzzo told CBC News he firmly believes the CIRB cannot suspend the legal right to strike.

Cavalluzzo pointed out that the CIRB was brought in to prevent an illegal strike by security screeners at Toronto's Pearson airport last week. He said the board only intervenes in legal strikes if there is illegal activity, and, even then, the board cannot stop the strike entirely.

"I don't think the CIRB has the authority to stop [a strike]

," he said.

But York University law professor David Doorey told CBC's Power & Politics with Evan Solomon that he believes the board does have that authority.

"The simple filing of this reference to the board has the effect under the statute of suspending the commencement of a strike," Doorey said.

"My take on it is it's pretty clear that in fact it does what the minister says it does."

Flight attendants have rejected 2 tentative deals

The flight attendants served a 72-hour strike notice on the airline on Sunday after 65 per cent of the votes cast were against the latest tentative collective agreement.

It marked the second time in recent months that the flight attendants have turned down a tentative deal with the airline.

They voted 87.8 per cent against ratifying the previous agreement in August.

Raitt has said a work stoppage would be unacceptable, and has indicated the federal government was prepared to use back-to-work legislation to end a strike by the flight attendants.

Parliament is not due to resume sitting until Oct. 17, meaning a strike could last a few days before legislation goes into effect. 

But a government source told CBC News that back-to-work legislation remains on the table.