PHOENIX (AP) — A 2010 state law designed to prevent Arizona from limiting greenhouse gases could prevent state regulators from coming up with a plan to limit carbon dioxide emissions from power plants without approval from the Republican-controlled Legislature, which has repeatedly opposed new federal regulations.

That means the federal government could be left to choose how to implement new air rules proposed by President Barack Obama this week. The U.S. Environmental Protection Agency rules are designed to allow state regulators to come up with the most efficient and least costly ways to cut carbon dioxide emissions.