The US Supreme Court said on Tuesday it will review national environmental standards requiring power plants to reduce emissions of mercury and other toxic pollutants.

The country's highest court received three complaints from 21 US states and industry groups protesting standards imposed in 2012 that require power plants to cut toxic emissions.

The complaints, lodged against the national Environmental Protection Agency (EPA), oppose the "huge costs" required to comply to the standards.

Supreme Court justices issued a brief written order saying they would consider whether the EPA "unreasonably refused to consider costs in determining whether it is appropriate to regulate hazardous air pollutants emitted" by power plants.

The justices met behind closed doors and considered the issue for an hour.

The EPA regulations require coal and oil-fired power plants to cut most emissions of mercury, which is considered especially harmful for children and pregnant women.

The challengers of the regulation include 21 states led by Michigan, a coalition of power plants and the US National Mining Association.

In April, a US Court of Appeals in Washington considered if the interpretation by the EPA was "appropriate and necessary," and ruled in favor of the regulations.

Judge Judith Rogers said the EPA was correct to prioritize "factors relating to public health hazards, and not industry's objections that emission controls are costly."

She said the regulation "properly puts the horse before the cart."

The Supreme Court will reconsider the decision of the Appeals Court when it examines the case in March for a June decision.