Environmentalists and the Bush White House have been teaming up at the Supreme Court today. Both are defending a clean air program that dates back to 1980.
On the other side is Charlotte-based Duke Energy, on the question of whether it has to put expensive pollution controls on its coal-fired plants.
A lawyer for Duke Energy told the court that government regulators suddenly changed their interpretation of the rules and sued the company.
The government and the environmental groups contend Duke and other utilities have long understood how the program works, but didn't comply.
Duke Energy appeared to get a boost from Justice Antonin Scalia, who calls it a "bit of an exaggeration" to say the rules were always interpreted the way the government says they were.