Normally, states aren't allowed to set their own car pollution rules that are stricter than federal ones—but California has special permission to ask for exceptions, called waivers, because of its long history of severe smog problems. The Environmental Protection Agency had granted California such a waiver for its "Advanced Clean Cars II" plan, which would require car makers to sell more low-emission and zero-emission (electric) vehicles in the state over time. This resolution would cancel that approval, meaning California could no longer enforce those specific stricter vehicle emission requirements. This matters not just for California drivers and car dealers, but for the country more broadly, since other states are allowed to adopt California's rules instead of the federal ones, so revoking the waiver could affect vehicle standards well beyond California's borders.