As the debate over the construction of the Keystone XL pipeline continues in the United States, a Canadian trade delegation is insisting that Canadian oil extracted from tar sands — the product that would be transported by an expanded pipeline — should not be classified as being dirtier than other types of oil.

Last week Canada’s natural resource minster, Joe Oliver, threatened to take the European Union to the World Trade Organization over its plans to classify oil harvested from tar sands as “highly polluting.”

“We are going to take whatever action we need to, and we may well go to the W.T.O.,” Mr. Oliver said at a news conference in Brussels. “We will defend our interests vigorously.”

Mr. Oliver made the comments on a visit to Brussels to negotiate an unrelated bilateral trade agreement.

Although the minister eventually backed away from his threat to take the issue to the top trade arbiter, the Canadian government is worried that the classification under the European Commission’s fuel quality directive could affect markets for the Canadian export.

“Canada’s oil sands are a major global resource — a resource that will make an increasingly strategic contribution to energy security and economic stability,” Mr. Oliver said in a ministry statement.

Both the Canadian hydrocarbon industry and government have been lobbying against the European fuel quality directive for years, according to a report by Reuters published this week.

The Canadian government argues that the directive unfairly penalizes Canadian oil.

The rules, which aim to help European countries reach greenhouse gas emission targets, classify global fuel sources by the emissions caused by their production and transportation.

Last week, a study commissioned by the provincial government of Alberta reported that oil extracted from the oil sands emit 12 percent more emissions than oil produced in Europe. Others estimate that oil coming from the oil sands is as much as 23 percent more polluting than other sources.

While Mr. Oliver was talking up Canadian oil last week, a Canadian-led group of climate scientists wrote an open letter to him criticizing the government’s energy plans. In one section, they write:

In short, we are not convinced that your advocacy in support of new pipelines and expanded fossil fuel production takes climate change into account in a meaningful way.

Avoiding further levels of dangerous climate change will require significantly reducing our reliance on fossil fuels and making a transition to cleaner energy.

The infrastructure we build today will shape future choices about energy. If we invest in expanding fossil fuel production, we risk locking ourselves in to a high carbon pathway that increases greenhouse gas emissions for years and decades to come.

Mr. Oliver’s European goodwill tour is directed to audiences on both sides of the Atlantic. With most of Canada’s oil exports currently going to the United States, the European bloc’s decision on how to classify the oil could affect Canada’s image as much as it does its bottom line.

“We don’t want the potential stigmatization and we’re quite concerned about that issue,” Mr. Oliver told Reuters last year.

This week, Mr. Oliver’s boss, Prime Minster Stephen Harper, is in New York to promote Canadian oil.

In an e-mail published by the Canadian press, Andrew MacDougall, the prime minister’s communication director, wrote: “As the prime minister has said before, the project will create jobs and economic growth on both sides of the border, and will provide a secure and stable supply of oil to the United States from a reliable partner and friend.”