Ken Lewenza's call came as thousands of union and community members gathered in London's Victoria Park for a mass rally.
Waving placards and chanting slogans condemning corporate greed, the protesters demanded an end to the three-week lockout of nearly 500 workers at Caterpillar's Electro-Motive plant.
"This demonstration is to send a message out to multi-national 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.
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.
Lewenza said earlier it's time for the 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."
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.