The ad features a 1969 print called "Hi-Ho, Silver," which shows a young woman in a cowboy hat and skirt straddling a fence. The caption says: "Still on the fence?" and encourages farmers to choose the wheat board for marketing grain.
But the National Farmers Union is questioning what an image of a long-legged woman straddling a fence has to do with selling grain.
Joan Brady, who heads the women's branch of the farmers union, says the image is used inappropriately.
"To me, I really didn't appreciate first of all, the image that it gave to rural women or women on the farm," Brady said in a phone interview from Manitoulin Island, Ont.
"Secondly ... if I was involved in a western wheat farm, I would be helping to make that decision to purchase contracts with the Canadian Board and that would turn me off pretty much very quickly because it dismissed me as a farm operator."
Dayna Spiring, the CWB's chief strategy officer, says the board believes there are many farmers who haven't decided what to do with their grain because of changes to the industry over the past year.
The CWB used to have a monopoly that forced western producers to sell through the board since the 1940s.
In late 2011, the federal government introduced legislation to end the monopoly. It means producers can now choose how to market their grain and one option is to continue going through the board.
Spiring says the ad, which started running in early January, is meant to be edgy.
"We wanted to be provocative, we wanted it to get attention, but it was certainly not our intention to offend anyone," Spiring said in an interview from Winnipeg.
"We have no plans to stop running it," she added.