Chris Buckley of CAW local 222 heads into a Whitby, Ont., court, where GM is seeking an injunction against the blockade of its Canadian headquarters in nearby Oshawa. (Mike Wise/CBC)

Union members from across Ontario gathered in Oshawa on Thursday to demonstrate against plans by General Motors to close a truck plant in the city.

Canadian Auto Workers union members were joined by members of other unions for what they called a "solidarity march" at GM Canada's headquarters.

GM announced last week that higher gas prices and steep declines in truck sales led to the surprise decision to close the plant by the end of 2009, putting up to 2,600 people out of work.

Just three weeks before the announcement, the automaker and the CAW had concluded a collective agreement aimed at saving jobs at GM plants in Ontario.

CAW president Buzz Hargrove said the company would violate that agreement by closing the plant, but GM officials maintained there are clauses in the deal that allow plants to be shut.

The automaker says U.S. truck sales in May were down 39 per cent from the same time in 2007.

Union, GM in court over injunction

CAW members have been blockading GM's headquarters in Oshawa, Ont., for more than a week to protest the automaker's plans to close a truck plant in the city. (J.P. Moczulski/Canadian Press)

Union members have been blockading GM's Oshawa headquarters since the closure announcement.

Thursday's rally in Oshawa came as the automaker and the CAW met in court in nearby Whitby to argue over GM's request for an injunction to quash the picket, and $1.5 million in compensation for lost business.

The company argued it believes the blockade is hurting its business, while the CAW maintained the company is breaking the collective agreement and that the blockade is the only way to get action.

The hearing was adjourned without decision until Friday.

Hargrove has said he expects union members will obey any court order to remove the blockade.

With files from the Canadian Press