Grain terminal workers at the port of Vancouver went on strike on Tuesday, halting shipments of about half of Canada's grain exports during the peak autumn shipping season.

The Grain Workers Union representing 650 workers at six Vancouver grain terminals - including those owned by Cargill, Richardson International and Viterra - accused employer Vancouver Terminal Elevator Association of having "invested very little effort in (contract) negotiations."

The work stoppage, decried by farmers, halts bulk shipments of canola, wheat, barley, oats and speciality crops. 

Last year, 52 per cent of all grain produced in Canada passed through the Pacific coast port.

The Grain Growers of Canada, an association representing 65,000 farmers, urged the government to intervene to bring an end to the strike, which it said risks having a "devastating impact on grain farmers."

Nearly 100,000 metric tons of Canadian grain arrive at these terminals each day, it said in a statement, and a shutdown will result in a loss of Can$35 million (US$26 million) in potential exports daily.

The Canola Council of Canada also said it was "deeply concerned about the work stoppage" in Vancouver. Its chief executive Chris Davison said it comes at a time when the industry is "already facing significant market challenges and headwinds."

China, the biggest buyer of Canadian canola, has said it is considering slapping duties on the oilseed crop used to make cooking oil, animal feed and biodiesel fuel, after Ottawa last month levied a massive surtax on imports of Chinese electric vehicles.