The union representing Air Canada employees on the verge of a strike said Monday it had made progress on some contract issues but had a long way to go on other key differences.

Roughly 3,800 sales and customer service staff could be on the picket line as early as Tuesday morning if differences on pension and wages aren't ironed out by midnight Monday.

CAW president Ken Lewenza suggested that 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 on Sunday, but hasn't yet heard back from the employer.

The proposal, Lewenza said, 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 being told that scheduled service will continue whether or not the airline's sales and customer service staff are 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 set to walk off the job just after midnight Monday.

In an interview from Montreal, airline industry analyst Karl Moore said that after 10 weeks of negotiations failed to reach an agreement, the strike action appears likely.

"It could turn around," Moore told CTV's Canada AM Monday. "But there are a couple of issues which really are important which I'm not sure we're going to get an easy resolution on."

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.

In Moore's view, this "legacy burden" poses a significant challenge for Air Canada given that it now has more retired employees than working ones.

But it's not a new problem. 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.

In the event workers do take to the picket lines, 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.

Despite the airline's pledge and preparations, Moore says some delays are inevitable.

"Management will have a good attitude, but if you're going to travel on Air Canada in the next few days go a bit earlier and be a bit patient," he advised, emphasizing the benefits of checking-in at home.

"Particularly if you have no baggage you can go straight through the security and to the gate."

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