Contract talks collapsed last week after locomotive maker issued a final offer that would cut the wages of union members in half, eliminate pensions and gut other benefits.
The previous contract for the more than 420 CAW members expired at the start of 2012, and the union set up picket lines at the plant Sunday evening.
Electro-Motive is owned by heavy equipment giant Caterpillar through its Progress Rail subsidiary. Caterpillar has a long history of playing hard ball with unions.
CAW president Ken Lewenza issued a statement blaming corporate greed for the lockout, calling it a serious attack on working people, their families and the greater London area.
"Caterpillar may be one of the richest corporations to ask for the deepest of cuts," he said.
Progress Rail, which also produces diesel-electric locomotives, opened a plant in Muncie, Ind. in October, leading to speculation it intends to relocate the London operation there to benefit from Washington's Buy American policies.
The CAW is asking the federal government to disclose the terms and commitments made during the 2010 purchase of Electro-Motive by Caterpillar, under the Investment Canada Act.
Ontario Federation of Labour president Sid Ryan says Ontario's labour movement is ready to mobilize to help the CAW stop scabs from crossing picket lines at the London plant.
"Workers across the province are angry and feel betrayed by their government and they are ready to fight together to defend good jobs," he said.
Ryan warned that corporations and all levels of government are being put on notice that 2012 will be marred by labour unrest if they continue to destroy the livelihoods of the middle class.
The OFL leader said the situation in London underscores the need for provincial legislation to ban the use of replacement workers during strikes and lock-outs.
Ryan also had a message for Ottawa, saying Prime Minister Stephen Harper's corporate tax cuts are continuing to fuel record profits that companies are keeping instead of investing in new technologies and equipment that lead to job creation.
The OFL represents 54 unions and one million workers in Ontario.