LONDON, ONT. - Prime Minister Stephen Harper and U.S. heavy equipment giant Caterpillar Inc. came under fire at a massive rally Saturday for locked-out locomotive workers in London.

Thousands of labour supporters poured into a downtown park in a show of support for the nearly 500 workers in the city entering their third week on the picket lines at Electro-Motive Diesel, an operating subsidiary of Caterpillar owned by its Progress Rail Services division.

Federal New Democrat Leader Nycole Turmel denounced Harper for "hiding" on the lockout issue and urged the EMD workers not to give up.

Ken Georgetti of the Canadian Labour Congress also slammed Caterpillar, which has remained silent during the three-week lockout and consistently declined interview requests.

"They want to take away what we have struggled to build for decades," Georgetti said, saying the EMD lockout has become the focus of labour acros Canada.

The lockout of the workers, members of the Canadian Auto Workers union, has been framed as a crucial battle for organized labour because of the issue that triggered it -- a contract offer that would dramatically cut many workers' pay and benefits. Wages at the plant, which exports locomotives around the world, range as high as $35 an hour. The union says the offer would cut wages in all job classifications, with the deepest cut about $18.50 an hour for half of the workforce.

CAW Local 27 president Tim Carrie kicked off the rally by asking the cheering crowd, "Are we ready to fight?"

Brianne Jones, the daughter of am EMD worker, denounced corporations that have cracked down.

"It's morally wrong to pay someone half their wage when the corporation is making billions," she said. "If they had their way, we would all be living in the slums." Jones said her father's wages have allowed her to go to university.

Carrie pointed out a long list of NDP MPs at the rally, along with London Liberal MPPs Chris Bentley and Deb Matthews -- both, cabinet ministers -- and NDP MPP Teresa Armstrong.

Many members of city council, including Mayor Joe Fontana, also showed up.

Auto workers, steelworkers and teachers flowed in from as far away as Timmins and Erie, Pa.

Long owned by General Motors, EMD has built thousands of diesel-electric locomotives shipped around the world.

The company was sold to an investment group after General Motors got out of the business, then bought in 2010 by Caterpillar through Progress Rail.

A global heavy equipment giant, known for hardnose dealings with unions, Caterpillar has hundreds of plants and 95,000 workers worldwide.

Sid Ryan, president of the Ontario Federation of Labour, which organized the rally, called Caterpillar "the poster child of corporate greed."

He warned the company not to take equipment out of the London plant.

"Let's link arms with the Occupy movement and build social justice in this country," he said.

Patti Dalton of the London District Labour Council said Caterpillar and the Harper government are getting a wakeup call.

"It's not that the government can't intervene -- they won't. They govern for the 1%," said Dalton noting London's near 10% unemployment rate -- the second-highest metro jobless rate in the nation.