FELICIA FONSECAFLAGSTAFF, Ariz. (AP) â¿¿ The U.S. Environmental Protection Agency was expected to meet a deadline Thursday on a plan to control emissions from three Arizona power plants that it contends have impaired visibility at places like the Grand Canyon, but a spokesman for the agency said the details wouldn't immediately be available. The EPA had proposed approving Arizona's air-quality plan to reduce sulfur dioxide and soot at the Cholla, Coronado and Apache coal-fired plants. But when it came to nitrogen oxide emissions, the EPA suggested the state's plan didn't go far enough and came up with one of its own. The conflict highlights the tension between the EPA and businesses after an election season in which the notion of heavy-handed environmental regulations became a popular argument for Republican candidates. Arizona and the administration of Republican Gov. Jan Brewer contend the EPA's proposals would cost hundreds of millions of dollars, causing utility rates to sharply increase for residents. Instead of low nitrogen-oxide burners, the EPA hinted it might require that some of plants' older units be equipped with selective catalytic reduction technology to keep 17,000 tons nitrogen oxide from being released into the air and causing visibility issues at 18 national parks and wilderness areas. Environmental groups contend the regulations are long-overdue and the benefits would extend not only to places like the Grand Canyon but to public health. They say the EPA's proposal is a step in the right direction. EPA regional spokesman Rusty Harris-Bishop in San Francisco said the agency would sign off on a plan late Thursday to meet a court-ordered deadline and would release details Friday. The EPA has said it proposed rejecting Arizona's plan for nitrogen oxide emissions because it didn't fully address the issues raised by the agency and federal land managers when it came to cost analyses, the best available technology for controlling emissions, and visibility benefits.