Canada has taken a notably tougher line with China over its ban on Canadian imports of canola seed, saying Beijing had provided no scientific evidence to justify the move and was hurting its own reputation.
China, citing the discovery of pests, expanded its ban on canola seed imports on Tuesday to include shipments from a second major exporter, Viterra.
Viterra is owned by Glencore's agricultural arm.
Earlier this month, Beijing halted shipments from Richardson International, Canada's top exporter of canola seed.
Canada's Liberal government and China have been locked in a trade and political dispute since the chief financial officer of Chinese telecom giant Huawei was arrested in Vancouver last December on a US extradition request.
China accounts for about 40 per cent of Canada's canola seed, oil and meal exports, according to the Canola Council, with seed exports to China worth some $C2.7 billion ($A2.8 billion) a year.
Canada's official opposition Conservative Party, which opinion polls show could win an election in October, says Prime Minister Justin Trudeau has not done enough to help canola farmers and is bungling ties with China.
"The restrictive measures imposed by China are said to be rooted in science. We have asked for the evidence," Public Safety Minister Ralph Goodale said in a statement.
"To date, none has been supplied. We will keep pushing as hard as we can on this vital point," added Goodale, who is from the western province of Saskatchewan, a major canola producer.
Trudeau said on Wednesday he was concerned about the ban and could send a delegation to Beijing.
He met with Richardson executives on Tuesday.
Goodale, using sterner language, said "measures that defy science and contravene sound business and trading practices detract from the good reputation for reliability which all trading nations seek to maintain."
The Chinese Embassy was not immediately available for comment.
