IN THE long war against margarine, the French-speaking province of Quebec, which contains half of Canada’s 12,500 dairy farms, remains an outpost of buttery resistance. Margarine cannot be displayed alongside butter on grocery shelves. Strict rules on the milk content of blended products preclude manufacturers from producing tastier versions of margarine, coffee whiteners and dessert toppings. Such tactics have worked. Butter accounts for 46% of retail sales in Quebec, well above the Canadian national average of 37.4%. But the vegetable-oil producers, which are mainly based in western Canada, have been gradually chipping away at their opponents’ defences. In 2005 a dispute panel under Canada’s Agreement on Internal Trade ruled that Quebec must remove its requirement that margarine sold in the province be a paler and less appetising colour than butter. Ontario, Canada’s other large dairy-producing province, was forced to remove its discriminatory rules in 2010. On January 8th the vegetable-oil brigade opened what may be the last battle in a campaign that dates back to 1886, with a new dispute-panel hearing on the remaining barriers erected by Quebec.

Should those barriers come down when the panel releases its decision in March, it will be a rare ray of sunshine in Canada’s otherwise gloomy internal-trade landscape. All ten provinces are guilty of impeding the internal movement of goods, services and people in Canada—sometimes on purpose, through the creative use of rules and regulations; and sometimes by accident when they fail to co-ordinate among themselves.

Recent trade disputes span multiple industries. A crane operator in Quebec found his licence was invalid in Ontario because it used a different title for his occupation—“hoisting engineer” as opposed to “crane operator” (or “grutier” in French)—and required three separate licences for different types of cranes whereas Quebec required just one. Manitoba complained that Ontario did not recognize the credentials of certified general accountants from other provinces and required them to be reassessed before they could practise in the province. Jim Flaherty, the finance minister, has been trying for almost eight years to create a single securities regulator in Canada to replace the 13 existing ones.

This might sound like small potatoes. But the federal government estimates that internal trade barriers cost the economy C$50bn ($46 billion) a year. Exporters complain that it is often easier to sell their goods and services abroad than to a neighbouring province. Almost 20 years after Canadian governments agreed to tackle these internal impediments, Canadian business groups say the problem remains. “The Canadian consumer market is relatively small to begin with and dispersed over a vast geographic area,” the main business groups said in an open letter to trade ministers last month. “It doesn’t make any sense to divide that market into fragments, each protected by meaningless regulatory barriers to trade.”

But meaninglessness is in the eye of the beholder. Local interests have plenty of significance for provincial governments: Quebec is more concerned to support its dairy sector than to unify the internal market in Canada. And the federal government, while maintaining that internal trade is a priority, is wary of picking provincial fights. So for now, progress on dismantling internal trade barriers will only be made one spreadable, vegetable-based dairy alternative at a time.