Leading U.S. independent refiner Valero Energy Corp faulted the decision. San Antonio-based Valero has six Texas refineries, the most owned by a single company. The plants employ 2,700 people. "When the flex permit program was rolled out in 1994, EPA and environmental groups applauded it, and EPA approval seemed implicit," said Valero spokesman Bill Day in a statement. "Now, 16 years later, EPA is reversing course, and our facilities are caught in the middle, creating significant uncertainty at a time when our economy can least afford it."