EDMONTON - Another four major U.S. companies are joining the move to either avoid or completely boycott fuel produced from Alberta's oilsands.

Walgreens, which has 7,500 drugstores across America, is switching fuel suppliers for its delivery trucks to those that don't make gas from oilsands crude.

"We found that it was a relatively simple process of surveying our vendors, seeing which ones may have tar sands oil sourcing and simply avoiding those vendors," said Walgreen's spokesman Michael Polzin. "We are in that process right now."

The Gap, Timberland and Levi Strauss have all told their transportation contractors that they will either give preference to those who avoid the oilsands or have asked them what they're doing to eliminate those fuels.

The move adds to growing international economic pressure on the oilsands industry and the Alberta government to reduce its environmental impact.

"What this signals is the beginning in earnest of the financial war over the tar sands," said Todd Paglia of the environmental group Forest Ethics, which is organizing the campaign.

As well, courier company Federal Express has promised it will consider the environmental and social impacts of the fuels it uses, although it didn't specifically mention the oilsands.

Polzin acknowledges that Walgreens isn't using much fuel from the oilsands.

"We had very little exposure to begin with," he said.

But the move fit with the company's other plans to reduce its carbon footprint, which includes energy-efficient buildings and some solar-powered stores.

It's also in tune with an American public looking to use its economic muscle to influence corporate policy, said Paglia.

"In the U.S., customers are increasingly saying we don't want to be part of the tar sands," he said.

Paglia admits the U.S. produces heavy oil of its own that isn't singled out in Forest Ethics' campaign. But he said the size and environmental impact of Alberta's oilsands as well as the plans to increase its import into the U.S. makes it an appropriate target.

"No, it's not 100 per cent fair," he said. "But there's nothing fair about what they're doing either."

Forest Ethics has organized successful economic campaigns before, including against companies logging old-growth boreal forests by targeting the customers of the pulp. Paglia said tracking oilsands fuel is much easier.

"It's tied to infrastructure," he said. "The pipeline goes somewhere and we can find out who's buying it."

Six Fortune 500 companies have now turned their backs on oilsands oil, including retailers Whole Foods and Bed, Bath and Beyond. Forest Ethics campaigner Nikki Skuce said she expects that total will reach about 13 in the coming months.

"Forest Ethics started this about a year ago, sending letters to Fortune 500 companies," she said. "There's more negotiations happening and more companies will be interested."

As well, a coalition of environmental groups are funding the so-called Rethink Alberta campaign. That effort has mounted billboards across the U.S. and England, targeting the province's tourism industry by suggesting the way it regulates resource development is threatening its natural beauty.

Industry and the Alberta government have responded with campaigns of their own, spending millions on TV and print ads detailing the hundreds of millions of dollars being spent on problems such as cleaning up the oilsands tailing ponds.

"We are having an impact because they are coming out with PR campaigns but no, I don't think we're winning," said Skuce.

"There's no action happening. The regulations aren't being put into place that are needed to reduce the environmental and social impacts that are happening."