Iowa Governor Kim Reynolds has blocked Iowa Attorney General Tom Miller from joining 21 states and six large cities in a lawsuit challenging a Trump administration policy easing restrictions on coal-fired power plants.
Miller says he sought approval from the governor in July, but Reynolds declined.
Miller, a Democrat, reached an agreement with Republican Governor Reynolds in May requiring him to get her consent before joining such lawsuits.
In exchange, Reynolds vetoed a bill lawmakers passed that weakened the attorney general’s powers.
Trump has replaced an Obama administration plan that required states to cut emissions from fossil fuel-burning power plants with a rule relaxing the state restrictions.
The federal lawsuit claims the Trump rule violates the federal Clean Air Act.