In United States v. DTE Energy Co. (DTE), the U.S. Court of Appeals for the Sixth Circuit held that EPA may use Clean Air Act New Source Review (NSR) to challenge a source’s preconstruction emission projection on narrow procedural grounds, but not to “second- guess” the projection’s substance. The decision is based on an incorrect interpretation of the NSR regulations and undermines the NSR program’s preconstruction review component. EPA should either change its regulations or clarify its interpretation of them, and adopt a litigation strategy to minimize the DTE decision’s unfavorable aspects and to persuade the Sixth Circuit to correct its errors. This will be important so EPA can continue using NSR, in concert with the proposed Clean Power Plan, to address air pollution from existing power plants.