Connecticut Gov. John Rowland vetoed the bitterly contested "Sooty Six" bill aimed at forcing the state's oldest and most-polluting power plants to reduce emissions.
The bill had been debated for four years as environmentalists and the electric power industry squared off.
"This is one of the more difficult decisions I've had to make as governor over the last seven years," Rowland said. "There's no one in Connecticut that does not want clean air."