Canada's natural resources minister has entered the fray over the proposed Northern Gateway pipeline with a controversial public letter accusing "radical" environmentalists of trying to delay the project and undermine the country's economic interests.

In an open letter released on the eve of the first public hearing on the proposal, Joe Oliver says environmentalists and other "radical" groups are trying to hijack the regulatory process.

More than 4,300 groups and individuals have signed up to speak at the regulatory panel hearings, which begin Tuesday in Kitimat, B.C.

"Their goal is to stop any major project no matter what the cost to Canadian families in lost jobs and economic growth," Oliver wrote in the letter. "No forestry. No mining. No oil. No gas. No more hydro-electric dams."

In an interview with CTV's Power Play on Monday, Oliver said he's concerned that some of the pipeline opposition groups are using American funds to further an "ideological" agenda.

Those groups are "attempting to game the system and create so much delay that the economic viability of the project would be undermined," he said, adding that Canada must expand its oil export market beyond the United States to take advantage of international prices.

The anticipated $5.5 billion Enbridge Inc. project would result in a 1,177-kilometre twin pipeline carrying crude oil from Alberta to an oil tanker port in Kitimat, B.C., for eventual export to Asia.

Oliver's letter was widely criticized by its targets and some policy analysts Monday, who said the minister should not be "demonizing" Canadians concerned about the pipeline's impact on environmentally sensitive land in British Columbia and Alberta.

In a letter responding to Oliver's comments, Sierra Club Canada executive director John Bennett said his group has worked with U.S. foundations on environmental campaigns that benefit both countries -- and there is nothing sister about that.

"The critical point to make -- and for Mr. Oliver to understand -- is the fact that Sierra Club Canada and other environmental organizations decide on policy and programs and then look for ways to finance them. It's not the other way around as Mr. Oliver suggests," Bennett wrote.

Several dozen First Nations groups have also said they will oppose the Northern Gateway project over concerns about the impact on their land.

Oliver said delegations should be whittled down to expedite the project approval process, especially if different groups are appearing before the panel with the same concerns and talking points.

Green Party Leader Elizabeth May told Power Play that those concerns are "legitimate" and nobody is trying to "foot-drag" the hearings.

The MP representing Saanich-Gulf Islands, B.C. alleges it was a Conservative government "propaganda machine," not Oliver himself, who wrote the letter attributed to him.

She said the letter makes "wild accusations," including allegations of foreign funds used to stymie the pipeline project.

May said the Enbridge project ultimately cannot be approved because it faces a "fundamental problem": putting oil tankers on the ecologically sensitive B.C. coastline, which has traditionally been protected from oil industry activity.

Oliver said that's why hearings will be held to ensure the pipeline is safe for the environment and affected communities.

He said the economic benefits of the project are undeniable.

"We're looking at the possibility of well over $3 trillion in economic development, hundreds of billions of dollars in revenue in the form of taxes and royalty payments to help finance our social programs, like health care and education and to create well over 600,000 jobs.

"This is in the national interest and it's urgent."