(Adds details on the strike, comment from Bombardier and background on the plant)
By Solarina Ho and Susan Taylor
TORONTO, July 14 (Reuters) - About 900 workers at Bombardier Inc's railcar production facility in Thunder Bay, Ontario, went on strike on Monday afternoon after contract talks hit an impasse over pension changes and benefit reductions.
The union, Unifor Local 1075, said its contract with Montreal-based plane and train maker Bombardier expired on May 31 and workers have been free to strike legally since June 10. No new talks are scheduled.
"We've rejected their last offer," Jerry Dias, president of Unifor, Canada's biggest private-sector union, said in an interview. "We have zero interest in that."
Bombardier's latest proposal would enroll new hires in a defined contribution pension plan instead of the current defined benefit plan, and workers who started after May 2010 would lose their post-retirement benefits, Dias said.
Union members at the Thunder Bay plant, which is in northwestern Ontario, held a three-day strike over similar pension issues in 2011 before Bombardier dropped the proposals.
"Bombardier Transportation is deeply disappointed that members of Unifor Local 1075 have made this decision to strike," said spokesman Marc Lefebvre, adding that the company felt it offered employees "a good contract proposal...that provides for well-paid jobs".
Lefebvre declined to provide details on how Bombardier would deal with the impact of the strike.
The Thunder Bay plant is currently working on multibillion-dollar contracts primarily for the Toronto area's transit system, including new subway and commuter-rail cars, and next-generation streetcars and light rail cars.
The union, which is concerned about production moving to Mexico, is also pressing Bombardier about the fate of some 300 plant jobs after a key rail program concludes next year.
"We can't even get straight answers from them about what they're going to be doing with the 300 people who may very well lose their jobs," Dias said. (Editing by Chris Reese; and Peter Galloway)