NDP Leader Jack Layton cast doubt on Stephen Harper's environmental policies as he flew over the Alberta oil sands in his campaign plane on Monday.

"We're looking at the largest source of greenhouse gas emissions in the world," he said, "and Mr. Harper is responsible because he is giving away the store to big oil companies."

Layton has demanded a moratorium on oil sands development, and criticized the "tax grab" it provides to oil and gas companies.

In a statement released on the NDP website Layton said: "Despite warnings from his own government agencies, Harper fast tracked Imperial Oil's Kearl tar sands development, north of Fort McMurray, without any conditions to mitigate the significant impacts on the environment."

From his campaign plane, flying above the oil sands, he pointed out a series of small toxic lakes. "The bottom line, and aboriginal people really believe this, is we can't drink oil."

The Alberta government defends the oil sands projects, saying that they're a vital part of the province's economy. Since 2006, the federal government has poured $14 billion into the projects, which has meant an over-$4-billion boon for Alberta. The province's website says that government and industry are committed to finding ways to reduce the impact of green house gases, and reduce the consumption of water.

In a response to Layton's accusations, Ontario Conservative MP Dean Del Mastro said the government has the projects under greater scrutiny and that the NDP leader is "attacking people where they work," since thousands of people rely on the oil sands for their jobs.

In his campaign stop statement Layton teased his "cap and trade" climate change policy, promising to "announce a plan that makes Canada's biggest polluters, including Mr. Harper's friends in big oil, pay for the pollution they create."

Alberta Premier Ed Stelmach said Monday that anything but a Conservative majority will put billions of dollars of proposed energy investments in jeopardy.

"Many of the investors around the world are looking for some stability and predictability in policy," Stelmach told reporters.

He warned all party leaders not to blame Alberta for the perceived ills of the environment. "Anytime we hear wrong information pointed at Alberta, I will speak up. We have work ahead of us in terms of working with all of the political parties to make sure they have the correct information."

Based on a report by CTV's Rosemary Thompson, with files from The Canadian Press