Thousands of union workers from across Ontario rallied in London on Saturday as they called for an end to the three-week-old lockout at the Electro-Motive plant — a contract dispute that could have major ramifications for trade unions across Canada.

Waving placards and chanting slogans condemning corporate greed, the protesters in Victoria Park demanded an end to the lockout of nearly 500 workers at the plant, which is owned by American heavy-equipment giant Caterpillar.

Ken Lewenza, head of the Canadian Auto Workers union, urged the company to return to the bargaining table.

"This demonstration is to send a message out to multinational corporations like Caterpillar," Lewenza told a cheering crowd Saturday.

"The message is clear," he said, that workers are coming together to fight for economic and social justice and defend good jobs increasingly under threat.

Demonstrators travelled from as far as Sudbury, Timmins and Ottawa to show support for the plant's employees, Lewenza said.

Caterpillar reporting record profits

The workers were locked out after they rejected a contract offer that would have cut wages in half and slashed benefits at a time Caterpillar is reporting record profits.

"It's important to us to see the amount of support that we're getting," said Luke Lewis, one of the locked out workers.

Another worker, Marty McKenney, said the lockout had put his entire life on hold.

"I'll stand [at the picket line] until this is either resolved or they close the damn plant," he said. "Just let me know what the hell you're going to do so I can pick up the damn pieces and get on with my…damn life."

Lewenza said earlier it's time for management to get back to the bargaining table and negotiate "a fair and equitable" contract.

He also called on the federal government to "stand up for Canadian jobs."

Conservatives silent on dispute

The federal Conservatives haven't commented on the lockout at the plant, which Prime Minister Stephen Harper once used as a backdrop to tout business tax breaks.

Meanwhile, Ontario Premier Dalton McGuinty, whose Liberals hold several seats in London, has said he is "very concerned" about the lockout and has offered to provide mediation.

CBC reporter Susan Pedler said from the rally that the average salary at Electro-Motive is $35 an hour, with the company demanding it be cut back to $16.50.

The company has hinted that if workers refuse the offer, they'll move the plant's work to Indiana, where similar pay cuts have already happened.

If Caterpillar wins the standoff, other Canadian employers will expect concessions as well, one labour expert says.

"It's discouraging, I'm sure, for many in the labour movement to see the CAW having losing battles over the last while," said Michael Lynk of the University of Western Ontario. "It's not to say that CAW doesn't remain a potent force. But if the CAW can't win these sorts of battles, then other unions may think, 'How can we win these battles?' "

With files from The Canadian Press