Minnesota regulators on Tuesday delayed approving new air pollution rules to protect natural areas after a taconite producer said they were too strict and might bring production to a halt.

The delay by the Minnesota Pollution Control Agency (MPCA) citizens board gives agency staff members another few weeks to address issues raised by Cliffs Natural Resources, operator of three taconite plants on the Iron Range.

Michael Long, director of environmental strategy for the Cleveland-based mining company, said at least one pellet-making line at its Hibbing, Minn., taconite plant would have a tough time complying with the proposed rules, which are meant to reduce haze caused by air pollution.

"In some cases it could require us to shut down altogether," he told the board.

Haze, or reduced atmospheric visibility, affects Voyageurs National Park and the Boundary Waters Canoe Area Wilderness (BWCA) in northern Minnesota and Isle Royale National Park on Lake Superior. The state is under a court deadline to come up with a long-term reduction plan under the federal Clean Air Act.

Minnesota's plan was criticized by nine of the 11 organizations that testified before the citizens board. Six conservation groups said the state's proposed haze rules were too weak.

The U.S. Forest Service and the National Park Service also objected, saying the rules would not improve visibility over parks and wilderness.

Haze is formed by emissions of nitrogen oxides and sulfur oxide, and can be seen at sunset or by comparing high-haze and low-haze photos. Power plants and other industries inside and outside of Minnesota are the sources of the emissions.

Minnesota's proposed plan would require the iron mining industry to use "good combustion practices" at six operations where iron ore is processed into taconite pellets.

That was criticized as too lenient by critics, including the National Parks Conservation Association. They advocate requiring taconite plants to install new low-nitrogen oxide burners, a relatively new technology.

Long said some of the state's emissions limits are "simply set too low and are unachievable," and would put one Hibbing Taconite line in violation 18 percent of the time.

Cliffs has asked for initially less-strict emissions limits that would be ratcheted down later as it gains experience with the new controls. State officials said they discussed those concerns with Cliffs, but could not reach a compromise. Now they will try again.

David Thornton, an assistant MPCA commissioner, said the haze regulations are the first stage of a decades-long effort to restore the air in natural areas to pristine conditions.

"We believe we have got a plan that takes the appropriate steps to do that," he said.

It wasn't enough for conservation groups, which argued that 11 Minnesota taconite operations and coal-fired power plants should upgrade to the best control technology for emissions.

"It's unconscionable that we would consider this adequate," said Christine Goepfert, a regional program manger for the nonprofit national parks association.

Under the state plan, five power plants implicated in the haze problem wouldn't be subject to plant-specific emissions restrictions, except for Xcel Energy's largest coal-fired plant, located in Sherburne County.

Xcel and Minnesota Power supported the state's haze plan. Xcel says it will spend $50 million to retrofit older units at Sherco and has dramatically reduced its statewide emissions thanks to earlier plant upgrades in the metro area.

David Shaffer • 612-673-7090