The labor actions would have halted services during a particularly busy week for Air Canada, as spring break shuts down many Canadian schools and families travel.

"We all know that it's March Break," Labour Minister Lisa Raitt told reporters. "We know this can have an effect on Canadian families, especially since this is a really peak travel season."

Raitt said the government had asked the Canadian Industrial Relations Board CIRB.L to consider whether a disruption at Air Canada would pose a health and safety risk.

There can be no work stoppage while the board is reviewing such a case. A similar move averted a strike by flight attendants in the fall, and Raitt said that case was not decided.

Government intervention undermines a union's ability to negotiate, said Paul Strachan, president of the pilot union.

"It's like negotiating with a monkey with the organ grinder standing behind you with a Sword of Damocles over your head," he said in an interview. "There's not much impetus on the monkey to bargain."

Air Canada had said it would lock out its 3,000 pilots at one minute after midnight on March 12, the time picked by its 8,600-member machinists' union to start a strike. Either stoppage could have grounded the airline.

Once the machinists gave notice, it forced Air Canada's hand, said PI Financial analyst Chris Murray.

"The company had nothing to lose by putting everyone on strike or in a sense taking everyone out," he said. "In for a penny, in for a pound."

Murray forecast that, like the flight attendants, an arbitrator would likely force the pilots and machinists to accept the tentative deals they have already voted down.

"We were hoping the minister wouldn't do this," said machinists' union spokesman Bill Trbovich. "We would just rather the system be allowed to go ahead and not have this interference."

It marks the third time in the past year the government has stepped in to stop or prevent a work stoppage at Air Canada.

Call center and customer service staff walked off the job for three days in June, but agreed to send a final sticking point to arbitration when the government threatened back-to-work legislation.

In October, flight attendants were on the verge of a strike when the government made its CIRB referral.

The carrier, which competes with WestJet Airlines (WJA.TO) on domestic and holiday routes and with foreign carriers to those destinations and others, wants to cut costs. It flies to some 150 destinations.

Before Raitt's announcement, a source close to the negotiations told Reuters Air Canada was in talks with the Air Canada Pilots Association and would meet with the International Association of Machinists and Aerospace Workers within 24 hours.

Last month, the pilots voted 97 percent in favor of a strike after rejecting a tentative offer. They are concerned by Air Canada's plans to set up a low-cost carrier, which they fear will hurt job security and wages.

The carrier's largest union, which represents mechanics, baggage handlers and cargo agents, issued a strike notice after talks broke off on Tuesday.

The machinists had also rejected a tentative four-year contract deal their union had reached with the airline, with the help of a government-appointed conciliator.

Shares of Air Canada rose 1.1 percent to C$0.94 on the Toronto Stock Exchange on Thursday.

(Additional reporting by Allison Martell, David Ljunggren and Louise Egan; editing by Janet Guttsman and Frank McGurty)

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