NEW ORLEANS - The Sierra Club, a national environmental group, is suing the Environmental Protection Agency to force the regulator to make sure Louisiana's coal-powered plants cut down on haze-causing pollution, and thereby clear up the skies above precious wilderness areas in Louisiana and Arkansas.

The lawsuit was filed Tuesday in U.S. District Court in Washington.

The suit charges that EPA has failed to take the necessary steps to impose measures to cut haze-causing pollutants being emitted from Louisiana's coal-fired plants. The suit contends the measures are mandated by the Clean Air Act.

In 2012, EPA rejected parts of a Louisiana state plan to clean up regional haze and the suit charges that the federal agency failed to come up with an alternative plan within a two-year deadline.