A group of prominent General Motors of Canada Ltd. dealers is suing the company and its parent General Motors Co., saying the auto maker has ignored their repeated pleas for financial help to address a dramatic drop in sales and market share.

GM Canada's market share in the Greater Toronto Area plunged more than 50 per cent between 2008 and 2013, hitting just 5.6 per cent last year, according to the suit by 17 Toronto-area dealers. The list of dealers includes operators of some of the biggest GM dealerships in the country and some whose relationship with the company goes back to the 1920s.

GM Canada (GMCL) and its parent, the suit alleges, have failed to offer the dealers financial help, while pumping millions of dollars into support programs forU.S. dealers in markets that are similar to Toronto. While Toronto area dealers' market share declined, U.S. dealers' market share grew, says a statement of claim filed in Ontario Superior Court last week.

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"GM responded to the problems faced by its American dealers by extending financial support and assistance, in accordance to its obligations to them, but GM and GMCL withheld similar support from Canadian dealers during a continuing decline in their market share," the claim says.

That decision threatens the Toronto dealers' long-term future, the claim says, even as the auto maker demands that the dealers spend up to $10-million each to redevelop their stores to meet new image standards set by the head office in Oshawa, Ont.

The lawsuit is an illustration of how the company's