Maine’s four American Indian tribes have joined a legal challenge to the federal Environmental Protection Agency’s mercury policies, calling the changes “grossly illegal.”

EPA aims to reduce pollution with several new programs, including a “cap and trade” program that limits the amount of pollution that can be produced, while allowing businesses to buy “pollution credits” from cleaner operations instead of installing pollution control equipment themselves.

A similar program has successfully reduced levels of sulfur dioxide, a main component of acid rain.

However, critics argue that the federal Clean Air Act requires that the EPA mandate the most stringent technology for cleaning up toxic pollutants. New equipment for drastically reducing mercury pollution is available – but was ignored by the EPA policy, they say.

In fact, the federal mercury rule specifically removes coal-powered plants – the major source of airborne mercury at 45 tons annually – from the list of industries that fall under the “best available technology” policy.

Eric Nicolar, air quality manager for the Penobscot Nation, said Tuesday the change only would increase the mercury pollution that already makes the fish located near tribal lands on the Penobscot River inedible.

“A lot of our tribal members just won’t eat fish out of the river – and we’re a river culture,” Nicolar said.

The tribes also argue they should have been consulted during the EPA’s rulemaking process on mercury – an issue they have raised informally several times without success.

That all four tribal governments agreed to become involved in the suit is significant – all are suffering the impacts of pollution, tribal leaders said.

“[Fishing] is one of the social and cultural ties that bind our tribal communities together,” said Brenda Commander, chief of the Houlton Band of Maliseet, in a statement released Tuesday. “That link has been stretched very thin because of mercury contamination.”

The attorneys general of 11 states – including Maine – filed suit against the mercury rule in May, calling the plan “deeply flawed.” Now the suit has grown to 14 states.

Environmental and public health groups, including the Natural Resources Defense Council, Physicians for Social Responsibility, the United States Public Interest Research Group and the Natural Resources Council of Maine, filed similar challenges last month.

Tuesday, the four Wabanaki tribes – the Penobscot Indian Nation, the Houlton Band of Maliseet, the Aroostook Band of Micmacs and the Passamaquoddy tribes at Pleasant Point and Indian Township – announced their intervenor status in the environmental coalition’s case. The tribes formally filed their petition May 27.