The company enacted a contingency plan the same day - contacting customers and re-routing its container ships to Halifax for cargo pickup.
"That is in motion," said Sid Hynes, executive chairman of the privately held Oceanex.
It's a plan he'd prefer not to activate.
"You shouldn't be able to shut down the second-largest port in Canada."
Oceanex moves about half the goods - including food, furniture, prescription pills and construction materials - that are shipped to Newfoundland.
As of Tuesday afternoon, Hynes said the contingency plan was working well.
"I'm pleased with everything I hear. It seems like it's kicking into gear and going the right way."
Oceanex operates three container ships. The Avalon and Cabot sail to St. John's each week from Montreal, while the Sanderling sails weekly from Halifax to St. John's and Corner Brook.
Hynes said most of his customers are opting to move their freight to Halifax for shipping.
"There's an awful lot of traffic moving towards Halifax on the road and rail, and we will move that out.
"The Sanderling has some excess capacity ... she's scheduled to depart on Friday and she'll clean that up."
The Avalon will likely sail next Tuesday.
Hynes figures rerouting cargo through Halifax will be more expensive for both Oceanex and its customers.
"It's a significant additional cost to move that cargo down to Halifax."
"There's such a big volume and you don't have a backhaul. And you need that equipment back up there (in Montreal) to bring more."
He doesn't foresee any problems actually shipping the extra cargo once it reaches Halifax, saying the company has plenty of capacity.
"Any one of our two ships can handle the same volume as we would do through Montreal."
On Monday, the Maritime Employers Association, which runs the Port of Montreal, locked out about 900 longshoremen who load and unload container cargo at the port. The move followed work-to-rule tactics by the longshoremen's union.
The two sides are scheduled to meet Thursday and Friday with the help of a federal mediator, said a spokesman for the Maritime Employers Association.
"The employers are ready to sit and get it solved as soon as possible," Gilles Corriveau said Tuesday, adding the talks could extend into the weekend.
"You shouldn't be able to shut down the second-largest port in Canada." - — Sid Hynes
He said the lockout will cost the employers association $800,000 per week.
However, there are also fears the lockout could be much more costly for businesses that use the port to get imported food and consumer goods.
Corriveau said containers full of goods, some of which could be perishable, were still sitting at the port.
At issue for the union is job security, as well as keeping guaranteed payments when longshoremen are on call and waiting for work.
The longshoremen have been without a contract since Dec. 31, 2008.
Union spokesman Daniel Tremblay said representatives are willing to meet with the mediator.
"We're still open to negotiations," he said.
Corriveau said businesses that depend on the port to get their goods in or out of Canada will have to decide how long they want to wait.
"Are they going to wait before shipping or are they going to reroute their stuff and have it shipped by another harbour or by another way?
"It could be airlines, for instance, for certain companies."
Corriveau said some ships are being redirected to Halifax, New York and Norfolk, Va.
The federally operated Port of Montreal has asked for a court injunction to limit the number of pickets.
Montreal, the country's second-largest port after Vancouver, says it generates spinoffs of some $2 billion annually, and creates more than 17,600 direct and indirect jobs.
Jackie Chow, chief executive officer of the Corner Brook Port, said she doesn't expect much disruption of service from the Montreal lockout.
The Oceanex Sanderling will be making its weekly trip to Corner Brook, she said. She expects the service to continue, but the amount of freight going through the port might change.
"I think they'll adjust to it," Chow said. "I think assets will be moved in to deal with it. As there's more demand for trucking and rail, I think assets will be moved into place to handle it."
email@example.com with files from The Canadian Press and The Western Star