New York and five other Northeastern states are suing federal regulators to force them to help ensure that upwind states control their pollution.
The suit against the Environmental Protection Agency was filed Thursday in Manhattan and has been joined by Connecticut, Massachusetts, New Hampshire, Rhode Island and Vermont.
They want a federal judge to force the EPA to add nine more states to the group required by law to act together to reduce smog in the Northeast.
By statute, the region consists of those six states plus Delaware, Maine, Maryland, New Jersey, Pennsylvania and the District of Columbia.
The smog-contributing states they want included are Illinois, Indiana, Kentucky, Michigan, Ohio, Tennessee, Virginia, West Virginia and North Carolina.
The EPA did not immediately reply to requests for comment.