The Canadian government was considering its options on Monday but made it clear that a strike at Air Canada would not be tolerated after flight attendants at the country's biggest carrier issued a 72-hour strike notice.

A strike starting on Thursday by 6,800 flight attendants at Canada's biggest airline "is unacceptable in this time of fragile economy," a spokeswoman for Labour Minister Lisa Raitt said.

"We are very disappointed with the result," the spokeswoman, Ashley Kelahear, said in an email after flight attendants, represented by the Canadian Union of Public Employees (CUPE), for the second time rejected a tentative labor contract with Air Canada. Results of the vote were released on Sunday.

Canada's Conservative government has weighed in twice already this year to halt labor action at Air Canada by starting to draft back-to-work legislation. Ottawa regards the airline as an important engine of economic activity.

Parliament is, however, is closed this week for the Canadian Thanksgiving break. An emailed question to the House leader as to whether members of parliament would be recalled to debate back-to-work legislation was not immediately answered.

A work stoppage by flight attendants would virtually ground the airline, analysts have said. Last month Raitt said a strike could strand as many as 65,000 passengers on its first day.

CUPE declined to comment on Monday on whether there were any plans for negotiations to resume with the airline.

Air Canada said overnight it remained hopeful "that a disruption can be avoided."

The airline has introduced a flexible booking policy to allow customers to change flight dates free of charge until Dec. 15. If there is a strike, it would operate a "partial schedule," Air Canada said.

A strike could start at one minute past midnight on Thursday. Some 65 percent of flight attendants who voted on the tentative labor contract rejected it.

Last month, the same flight attendants overwhelmingly rejected a previous labor pact.

A key sticking point in the negotiations have been work rules, notably cabin crews' demands for more payable hours during stopovers. Some flight attendants are also unhappy about Air Canada's plans to start up a low-cost carrier, where lower pay scales will apply.

Canadian markets were closed on Monday for the Thanksgiving holiday.