The Sierra Club is taking on the kings of the soft-drink world.

The environmental group and the conservation group ForestEthics are running ads in USA Today this week that call on Coca-Cola and Pepsi to end their reliance on fuel derived from Canadian oil-sands crude when shipping their products around the U.S.

“Shipping soda to store shelves takes a lot of oil — in fact the soda industry is one of the biggest oil users in the United States,” say the ads. The ads assert that “despite promises of sustainability,” Pepsi and Coke are using “one of the dirtiest oils on Earth, carbon-intensive Canadian tar sands.”

The ad targeting Coca-Cola will run in Atlanta, where the company’s headquarters are located. The ad targeting Pepsi will run in the Dallas area, where PepsiCo has some of its corporate offices.

The ads are part of the Sierra Club’s Tastes Like Tar Sands campaign, which specifically targets Coke and Pepsi.

“Your industry’s vehicle fleets total more than 100,000 cars and trucks,” the campaign, which is also sponsored by ForestEthics, says on its website. “Choices you make about … how your company sources oil, and the efficiency of your fleet, will have a direct effect on U.S. carbon pollution and will send powerful market signals about efficiency and extreme oil.”

The groups are calling on Pepsi and Coke to use their status as major U.S. companies to alter their contracts with fuel and transportation providers to require that their fuel come from refineries that do not rely on oil sands. ForestEthics has identified 60 U.S. refineries that process Canadian oil sands into fuel.

A Coca-Cola spokeswoman declined to comment directly on the ads, but the company issued a statement touting its efforts to reduce its carbon footprint “by improving the efficiency of our manufacturing and distribution processes.”

“We’ve improved the energy efficiency of our global manufacturing operations by 18 percent since 2004,” the statement said. “We’re proud to operate the largest hybrid electric commercial truck fleet in North America. We will continue these efforts as we work toward our goal to reduce our carbon footprint embedded in ‘the drink in your hand’ by 25 percent throughout our value chain by 2020.”

PepsiCo did not respond to a request for comment.

Christopher Gindlesperger, a spokesman for the American Beverage Association, said the industry has made major strides in reducing emissions from its vehicles.

“Moving forward, our industry will continue working together and with interested parties to ensure that our leadership and innovation across a broad selection of the environmental platforms further strengthens the commitment to our consumers, customers, communities and our planet,” Gindlesperger said.

The Sierra Club and ForestEthics acknowledge that ending companies’ reliance on oil sands isn’t always easy, but they say major corporations like Pepsi and Coca-Cola should take the lead.

“In some parts of the country where most refineries process tar sands, this is difficult or impossible,” the campaign website says. “However, in many areas of the country, it is quite feasible to switch to fuel that comes from refineries that don’t use oil from tar sands.”

Tastes Like Tar Sands is just one slice of the Sierra Club’s and ForestEthics’ broader push to persuade other major companies to clean up their corporate vehicles though the Future Fleet program. Activists say 19 companies have committed to addressing the environmental footprint of their transportation fleets.