A consumer-rights group is arguing that a Supreme Court decision handed down in June undercuts President Trump’s claim that the International Emergency Economic Powers Act gives him sweeping tariff authority, escalating a long-simmering fight that has previously focused on how lower courts should interpret that ruling into a push for the justices to explicitly say what it means for tariffs. Consumer Watchdog, a nonprofit consumer-protection organization, filed an amicus brief in the Supreme Court litigation over Trump’s IEEPA tariffs on...