More than 600 workers at a freight rail car assembly plant in Hamilton, Ont., are on strike after voting against the company's final contract offer.

The workers at National Steel Car Ltd. walked off the job on Monday after rejecting the company's offer by a margin of 95 per cent, the union representing them said.

Grantley Howell, spokesman for United Steelworkers Local 7135, told CBC News the company wants the workers to waive their seniority rights and accept a 25 per cent hourly wage cut.

"It is a pretty grim sign," he said. "You've got guys who've been there 30 years … who don't even think they are going to be able to retire."

More than 1,700 people have been laid off from the Hamilton plant since 2006. The remaining 660 workers were on four-day workweeks.

In a statement, National Steel Car said it must take "dramatic steps" to reduce costs in order to remain competitive in world markets.

"The company currently has no firm orders and the market outlook remains poor," the statement said.

National Steel Car is expanding in the United States by building a $350-million manufacturing plant in Alabama.

The union has accused the company of seeking to transfer operations from its Hamilton plant to the Alabama facility once it is completed.