TORONTO - Air Canada's customer service workers are back on the job, but there's the possibility of more work stoppages to come, as the airline remains in contract talks with several other key employee groups.

Pensions and wages, which prompted counter staff and reservations personnel to hit the picket lines, are expected to feature in upcoming negotiations with the airline's flight attendants, pilots, mechanics and baggage handlers.

The workers, represented by the Canadian Auto Workers union, returned to work Friday after a three-day strike. The two sides came to an agreement Thursday, shortly after the federal Labour Minister Lisa Raitt prepared back-to-work legislation.

Air Canada's (TSX:AC.B) next round of negotiations is with the union representing 6,800 flight attendants, who are currently waiting for a federal conciliator, which should be appointed next week.

The union says the flight attendants could be in a legal strike position by mid-August, but Air Canada -- which says it looks forward to negotiated settlements with all its labour groups -- says the legal strike position isn't before September.

The airline was able to maintain its schedule, albeit with some delays, despite the strike by the counter staff and reservations personnel, but a strike by flight attendants would cause a far greater disruption.

Meanwhile, Air Transat flight attendants are in a legal strike position as of July 20, but the company said it is positive about the way negotiations are going.

The International Association of Machinists and Aerospace Workers union representing mechanics and baggage handlers at Air Canada will be back at the bargaining table in July.

Air Canada and its pilots union are also set to return to the bargaining table after union members rejected a tentative agreement earlier this year.

"We're not in serious bargaining with the IAM and we're not at the table with the pilots and none of those other groups are close to the strike, certainly not this summer," an Air Canada spokesman said.

"We're very satisfied with the progress with the various union groups so far and we're looking forward to getting negotiated settlements with all our labour groups."

The unions each say the main issue is over the establishment a defined contribution pension plan for new hires, instead of the current defined benefit plan -- the same sticking point as with the customer service workers.

With defined contribution plans, the company's contribution is limited to a set, negotiated amount and payouts to retirees depend on the performance of the underlying investments. Defined benefit plans require a set amount to be paid to retirees.

George Smith, a labour expert at Queen's University, said the first collective agreement settled between a company and a union sets the framework for other upcoming negotiations with others. That usually makes it easier to come to a settlement, but each group has its own individual issues to cover depending on the nature of the work that union members do.

"There may be elements of the negotiation that involve a trade off that are different for one unit or another that can have an impact on any kind of pattern that might be set," he said.

Dave Ritchie of the International Association of Machinists and Aerospace Workers said the threat of back-to-work legislation interferes with the union's ability to bargain freely, but the union is positive a deal can be reached.

The union represents 12,500 baggage handlers and mechanics, with finance and clerical staff each being in separate bargaining units.

"We're going in there with the full expectations of coming out with a full collective agreement that both our union and the company can live with," he said.

Meanwhile, the union representing some 1,500 Air Transat flight attendants has also asked for a federal conciliator to help after 95 per cent of union voters rejected the airline's latest offer.

CUPE said the Air Transat flight attendants will be in a legal strike position as of July 20. Collective agreements with baggage handlers and pilots have already been settled.

The main sticking points are an increase in the number of work hours and wages, the union said.

"We certainly do not want to disrupt the operations of the company this summer and we are focused on negotiating a settlement as quickly as possible," Nathalie Stringer, president of the Air Transat component of the union said in a statement Thursday.

The contract expired in November and negotiations are set to resume Tuesday.

"So far we've got a lot to do and we're looking to resume negotiations at a very positive mindset," said company spokesman Pierre Tessier.

Ian Markham, who heads Canadian retirement research at consultancy firm Towers Watson, said there are going to be more labour disputes in the future over pensions plans in the country.

He said that companies more than 50 years old are most susceptible to pension funding shortfalls and are the most likely to try to convert their pension plans.

"What I think we're going to actually see more of is organizations seeking not only to do something similar for future hires but to seek to apply some kind of new pensison arrangement for workers who are already covered by the pension plan now," he said.