The Supreme Court is stepping into a new case about Obama administration environmental rules, agreeing to review a ruling that upholds emission standards for mercury and other hazardous air pollutants from coal- and oil-fired power plants.

The justices on Tuesday said they would hear arguments from industry groups and states that are challenging Environmental Protection Agency rules designed to clean up chromium, arsenic, acid gases, nickel, cadmium as well as mercury and other dangerous toxins.

The pollutants contribute to respiratory illnesses, birth defects and developmental problems in children.

The federal appeals court in Washington, D.C., upheld the rules in April.

One judge on the appeals court complained then that the EPA didn't consider costs in deciding whether regulation of hazardous air pollutants from power plants is appropriate.

"The problem here is that EPA did not even consider the costs," wrote Judge Brett Kavanaugh of the U.S. Circuit Court of Appeals for the District of Columbia. "And the costs are huge, about $9.6 billion a year -- that's billion with a b -- by EPA's own calculation."

The other two judges on the appellate panel said in response that the EPA properly looked only at health risks, not compliance costs, in deciding that mercury and the other pollutants should be regulated.  But the agency did factor in costs and benefits at the next step, when it wrote the standards that the plants need to meet, the court said.

EPA determined that when the rules are fully in effect in 2016, their benefits will exceed the costs by a factor of at least 3 to 1. Some industry groups have said the EPA was overstating the benefits.

The Supreme Court said it wants to know whether EPA unreasonably refused to consider costs in the first place.

About half the coal-fired power plants in the United States were built more than 40 years ago and have never installed advanced pollution-control technology, EPA said.

The agency first decided to go ahead with the limits on power plant emissions in 2000, the final year of the Clinton presidency.

But after President George W. Bush took office in 2001, EPA tried to undo its earlier decision. The circuit court, however, blocked EPA from doing so. And when Barack Obama became president in 2009, the agency again decided to move forward. It issued final rules in 2012.

Twenty-one states are taking part in the Supreme Court appeal. They are: Alabama, Alaska, Arizona, Arkansas, Idaho, Indiana, Iowa, Kansas, Kentucky, Michigan, Mississippi, Missouri, Nebraska, North Dakota, Ohio, Oklahoma, South Carolina, Texas, Utah, West Virginia and Wyoming.

The case will be argued in late March, with a decision expected by the end of June.