The US Supreme Court is grappling with a case that has put it in a direct face-off with US President Donald Trump’s signature economic policy — the sweeping global tariffs. The court’s decision is set to define the limits of presidential power in the US.ARTICLE CONTINUES BELOW VIDEOOn November 5, the nine judges of the US Supreme Court heard arguments on the legality of these tariffs. The outcome will not only determine the fate of a policy with immense economic consequences but also test the court’s own consistency on the recently innovated legal principle known as the “major questions doctrine”.What are Trump’s tariffsSoon after returning to the White House earlier this year, President Trump began imposing tariffs on goods from nearly every country. He invoked a 1977 law – the International Emergency Economic Powers Act (IEEPA), which allows the president to regulate international commerce during a national emergency.Trump declared two such emergencies: one related to the trafficking of fentanyl and other drugs into the US, and another concerning the country’s longstanding trade deficits.Citing these, he imposed tariffs – ranging from 10 percent on most goods to 50 percent on certain Indian exports and well over 100 percent on some products from China.However, the challengers – a coalition of small businesses and a dozen US states – claim that the IEEPA does not explicitly mention the words “tariffs”, “duties”, or “taxes”. They argue that the President has overstepped his authority, using a law meant for specific emergencies to unilaterally overhaul the country’s entire trade policy – a power the US Constitution gives only to Congress.Three lower courts have already ruled against Trump, finding his use of IEEPA to be illegal. The Trump administration appealed these decisions to the Supreme Court.Story continues below this adWhat is ‘major questions doctrine’This is the central legal principle at play. The major questions doctrine is a rule of interpretation that the US Supreme Court had first referred to in 2000 but formally named and applied only in its 2022 decision in West Virginia v Environmental Protection Agency. According to the doctrine, if an executive agency wants to decide on an issue of “vast economic and political significance” – a “major question” – it must have clear, direct and explicit authorisation from the US Congress.In other words, the executive branch cannot rely on vague or general language in an old law to justify a massive new policy.This is especially significant given the court’s current composition. Appointments to the US Supreme Court are made by the President and are often intensely political, with the current composition tilted 6-3 in favour of the Republicans.This conservative majority has used the major questions doctrine decisively in recent years to strike down major policies of the previous Biden administration, including a COVID-19 vaccine mandate and a $430 billion student loan forgiveness programme.Story continues below this adChallengers argue that the same logic must apply to Trump’s tariffs. The economic impact is estimated to be in the trillions of dollars — far exceeding the student loan programme the court deemed “staggering by any measure”.Since the IEEPA does not explicitly grant the power to impose tariffs, they argue, the President’s actions are illegal under the doctrine.The hearingDuring nearly three hours of arguments at the November 5 hearing, many Supreme Court judges — including key conservatives — appeared sceptical of the Trump administration’s position.The government’s counsel, Solicitor General Dean John Sauer, argued that the power to “regulate importation” under IEEPA was broad enough to include tariffs. He also suggested that the major questions doctrine should not apply in matters of foreign policy and national security, where the President has inherent authority.Story continues below this adSeveral judges – including conservative Chief Justice John Roberts – pushed back. Chief Justice Roberts noted that tariffs were a form of tax, and taxation has “always been the core power of Congress”, describing the administration’s justification for using IEEPA as a “misfit” for the vast authority it was claiming.Justice Neil Gorsuch, a Trump appointee, worried that upholding the tariffs would create a “one-way ratchet toward the gradual but continual accretion of power in the executive branch”, while Justice Amy Coney Barrett — another Trump appointee – asked Sauer to point to any other time in history where the phrase “regulate importation” had been used to grant tariff-imposing authority.The court’s liberal justices also voiced deep scepticism, with Justice Ketanji Brown Jackson pointing out that IEEPA was originally intended to constrain presidential emergency powers, not expand them.What’s at stakeThe court’s decision will have profound implications.Story continues below this adIf it strikes down the tariffs, it would deal a major blow to Trump’s agenda and could trigger a constitutional confrontation between the judiciary and an executive that has repeatedly warned of “ruinous” consequences from an adverse ruling.However, if the court upholds the tariffs by choosing not to apply the major questions doctrine, it would face accusations of political hypocrisy and would open itself to the criticism that the doctrine is used selectively.