They say there is no proof the measure is necessary.
Robert MacKinnon told a judge in Winnipeg on Wednesday that lawyers representing former directors of the wheat board haven't backed up their demand for an injunction.
They haven't shown the new law will cause irreparable harm or provided proof that justifies overturning the will of democratically elected officials in Parliament, he said.
"We say this motion should be dismissed," MacKinnon told a packed courtroom. "The plaintiffs have failed to satisfy the heavy onus that lies on them."
Justice Shane Perlmutter reserved his decision.
The eight one-time wheat board directors were elected by farmers and were dismissed when the federal government's bill ending the monopoly was passed late last year. They want implementation of the new law stopped until a court rules on its validity. They say the law isn't valid because the government didn't hold a referendum among producers before ending the monopoly.
The federal government has argued that farmers have a right to sell their grain independently and Parliament can change its own laws. MacKinnon said the new law repeals the old one so the government was never bound by the clause requiring a referendum.
The former wheat board directors also haven't proven anyone will be hurt by the new law, he added. Many grain producers are in favour of abolishing the monopoly, he said.
There is no conclusive proof that anyone will lose money because there is no consensus that the wheat board monopoly guaranteed farmers got the best price for their grain, MacKinnon argued.
"Clearly (they) are not representing all farmers," he told the judge. "They're representing eight people."
The former board members losing their jobs doesn't constitute irreparable harm, he said.
The bar for interfering with an act of Parliament is high, suggested MacKinnon, who added the evidence put forward by the former directors doesn't pass the test.
MacKinnon also pointed out that the judge's injunction would only apply to Manitoba, and would lead to confusion and a patchwork of different law across the Prairies.
"The balance of convenience clearly favours a continuation of the new act."
Lawyer Colin MacArthur, who represents the former wheat board directors, argued the judge should give them extra weight since they were elected by farmers who wanted the wheat board to maintain its monopoly.
"The legislation coming into effect will create irreversible changes to the Canadian Wheat Board and those changes will irreparably harm, not only us, but producers in Western Canada," he argued. "Clearly it is all producers who have been disenfranchised improperly by the refusal of the minister to perform what he was obligated to do."
The hearing is the latest chapter in the continuing battle over the new law.
Since the 1940s, Prairies farmers have had to sell their wheat and barley to the board, which in turn exported it to foreign markets. Despite vocal opposition and several lawsuits, the federal government went ahead with a long-standing promise to abolish the monopoly.
The government aims to have an open market for wheat and barley by the next crop year starting Aug. 1.
Last month, former wheat board directors won the first round of the court battle. A Federal Court justice ruled the government's bill to amend the wheat board act violated the law because no plebiscite was held.
But Justice Douglas Campbell also made it clear that his ruling was just a statement on the government's actions. He said he would not interfere with the legislative process and did not order the government to reverse its decision.
The directors are hoping to use Campbell's ruling to get another court order that would force the government to withdraw its changes.