Air Canada's 3,800 sales and customer service employees are on strike, after late-night contract negotiations failed to reach a deal on two main issues: pensions and wages.

The workers will be on the picket line Tuesday.

Earlier on Monday, hours before the midnight strike deadline, CAW president Ken Lewenza had suggested that an agreement was a long shot.

"We did a lot of work but it just seems to me that we should be moving a little bit quicker than we are right now," Lewenza said.

He said the union put forward a proposal that would achieve pension security and guaranteed wage increases after 10 years of uncertainty. But he offered no further details.

Meanwhile, Air Canada ticket holders were told that scheduled service would continue regardless of the airline's sales and customer service staff walking the picket lines Tuesday morning.

But would-be travellers were advised to plan ahead if they want to avoid delays.

In total, 3,200 airport customer service agents and 600 call-centre staff are walking off the job.

Chief among the sticking points is Air Canada's proposed changes to workers' pension plans.

Under the suggested changes, new employees would sign onto a "defined contribution" pension that would see them collect a set, pre-determined lump sum at retirement.

But the Canadian Auto Workers local representing the workers would rather stick with the present "defined benefit" pension plan that gives retirees regular, predictable payments. While employees typically favour the ongoing benefits of the latter plan, employers can find themselves saddled with additional costs if their pension fund runs short.

Air Canada was forced into creditor protection in 2003 due in part to the cost of the company's pension deficit. That figure stands at $2.1 billion today.

Air Canada's unions agreed to a number of concessions when the company restructured back in 2004, but left the defined-benefit pension plans untouched. And CAW president Ken Lewenza told CTV News his members aren't willing to negotiate those benefits away now either.

"We bargained these pension plans over four decades ago and as a result of the global financial crisis and a top-heavy salary structure for CEOs, we're being asked to feel the pain," Lewenza told CTV News Channel as negotiations continued at a downtown Toronto hotel through the weekend.

Both the airline and the union have maintained they want to avoid a strike and federal Labour Minister Lisa Raitt has weighed in too, urging both sides to reach a deal or risk impacting Canada's economic recovery.

Air Canada has promised to enact a contingency plan aimed at ensuring that flights continue to take off and land as scheduled.

"All bookings will be honoured," the airline said in a statement posted to its website.

"Management has been trained to provide assistance at the airports that would be affected," the airline explained, warning also that anyone planning to check-in at the airport's self-service kiosks should expect longer-than usual lineups.

Travellers who want to avoid delays are nevertheless advised to familiarize themselves with Air Canada's online self-service tools for booking tickets, making changes and obtaining boarding passes.

Air Canada says if its workers go on strike, the airports in Vancouver, Calgary, Edmonton, Winnipeg, Toronto Pearson, Ottawa, Montreal, Halifax and St. John's, NL will be affected.

With files from The Canadian Press