Seven Northeastern and mid-Atlantic states announced plans Tuesday to sue the Environmental Protection Agency, saying it is violating the Clean Air Act by failing to address methane emissions from oil and gas drilling, which has boomed in Pennsylvania and West Virginia.

The EPA is violating the Clean Air Act by failing to address the emissions. Methane is a potent greenhouse gas, and the oil and gas industry is the largest source of emissions in this country. Other major sources come from landfills and livestock.

Howard Feldman, a spokesman for the American Petroleum Institute, said the lawsuit "makes no sense" since the EPA passed rules on oil and gas emissions earlier this year, and many companies have already started installing new equipment to limit methane leaks and other pollution. Those rules take effect in 2015.

It's not clear whether New York is also taking extra steps to limit methane emissions from other sources. While the EPA estimates that the oil and gas industry is responsible for 37 percent of the nation's methane emissions, landfills are responsible for 16 percent, and livestock such as cattle and pigs contribute 21 percent. Some natural gas leaks also occur not just at wells, but from distribution networks in cities.