Mary Dawson says Tory MPs who are involved in grain farming are free to vote on a government bill to scrap the Canadian Wheat Board.
While they have a personal interest in seeing the bill passed, Dawson says it's an interest "that is shared with a broad segment of the public."
As such, it's excluded from the conflict of interest code for members of Parliament, which prohibits MPs from voting on a matter that could further their private interests.
The bill would put an end to the wheat board's monopoly on wheat and barley sales in western Canada.
The Harper government contends the move will result in western farmers being paid higher prices for their crops.
Both the NDP and Liberals had asked Dawson to look into allegations of conflict of interest after a number of Tory MPs made no secret of the personal benefit they stood to gain from passage of the bill.
They had argued that at least seven, and possibly many more, Tory MPs should recuse themselves from voting on the bill — which could have cost the government majority support for the measure.
New Democrat MP Pat Martin called Dawson's ruling Wednesday "a disgrace."
"Conflicts of interest fuel the cynicism of an already jaded electorate and her ruling certainly leaves to stand the appearance of conflict," he said.
He questioned how grain farmers, which he said make up 0.2 per cent of the population, could be considered a broad segment of the public.
"Our ethics commissioner never seems to find anything wrong with anything that anybody ever does. I don't know how this could be any more straightforward."
But Agriculture Minister Gerry Ritz welcomed Dawson ruling and blasted the NDP for trying to block the wheat board bill.
"Once again, the NDP show how disconnected they are from western Canadian farmers and how they will do anything to prevent western farmers from having marketing freedom," Ritz said in comments issued by his office.
"In line with the decision by the ethics commissioner, our party will be standing up and voting as the only party that truly represents western Canadian farmers."