Wisconsin is joining a lawsuit nine other states filed last month challenging new regulations issued by the federal government that critics say fail to protect children and expectant mothers from the dangers posed by mercury emissions from power plants.

Attorney General Peg Lautenschlager, who testified against the rules last year during a federal hearing in Chicago, said Friday the state has been looking for a vehicle to challenge the rules and found it in the multistate suit.

Lautenschlager said mercury was particularly a problem in Wisconsin, where 90 percent of the lakes and streams have high levels of the toxin and the population eats more fish than the national average.

"If those fish are coming from lakes with mercury levels that are high, it obviously poses dangers," Lautenschlager said.

The lawsuit, filed in federal court in Washington, D.C., said the new federal rules announced last month by the Environmental Protection Agency do not go far enough to satisfy Clear Air Act requirements.

The regulations aim to cut mercury emissions from coal-burning power plants by nearly half within 15 years, but opponents say the plan provides an out for the worst polluters by allowing them to trade "pollution credits" with cleaner plants.

State officials have said the new regulations would force Wisconsin to weaken more stringent state controls that were implemented last year.

The state rules require major power plants to cut mercury emissions in two phases - by 40 percent by 2010 and by 75 percent by 2015.

Lautenschlager said her office mailed the state's brief to the Washington, D.C., court last week. The attorney general needs authorization to file such an action from the governor or a house of the Legislature. Lautenschlager said her office mailed the brief prematurely, but the governor has now pledged to authorize the suit, which will validate the filing.

Doyle planned a news conference in Milwaukee Monday to announce his approval of the suit.

Under the EPA's plan, each state is given a pollution limit and then places caps on its plants. Those that exceed the limit can buy pollution credits from plants emitting less mercury pollution than they are allowed.

The program begins in 2010, but utilities do not have to do anything specifically to control mercury until then.

The New Jersey attorney general's office is taking the lead on the lawsuit. The suit criticizes the EPA for exempting power plants from having to install the strictest emissions control technology available. That technology would cut mercury pollution by 90 percent, according to the New Jersey attorney general's office.

The eight other states involved in the suit are California, Connecticut, Maine, Massachusetts, New Hampshire, New Mexico, New York and Vermont.