Global markets watch closely as Supreme Court weighs legality of Trump’s tariffs

The US Supreme Court is expected to deliver rulings on Friday in a set of high-stakes cases that could carry far-reaching consequences for the American economy, global trade, voting rights and free speech, according to court disclosures and reporting by Reuters.

Among the most closely watched matters is the legal challenge to President Donald Trump’s sweeping global tariffs, a case that has emerged as a major test of presidential authority. The court signalled on its website earlier this week that it may issue decisions when the justices take the bench during a scheduled sitting, though it does not specify in advance which rulings will be released.

The tariffs case stems from Trump’s decision to invoke the International Emergency Economic Powers Act (IEEPA), a 1977 statute traditionally reserved for national emergencies, to impose duties on imports from multiple countries. Trump justified the move by citing concerns over persistent US trade deficits and, in the cases of China, Canada and Mexico, the need to exert economic pressure to curb the flow of fentanyl and other illicit drugs into the United States.


Lower courts, however, ruled that Trump’s use of the law exceeded his authority, prompting appeals by his administration. During oral arguments heard on November 5, both conservative and liberal justices expressed scepticism about the legality of the tariffs, raising questions about whether trade deficits qualify as a national emergency under the statute, Reuters reported.

Trump has publicly warned of serious consequences should the court strike down the tariffs, repeatedly arguing that the measures have strengthened the US economy and enhanced national security. The Republican president has continued to defend the policy in recent social media posts.

The financial stakes are significant. According to data from US Customs and Border Protection cited by Reuters, Trump’s administration could be forced to refund more than $133.5 billion in tariffs to importers if the Supreme Court rules that the duties imposed under IEEPA are unlawful. That figure represents the total assessed through December 14 on imports since the tariffs were first imposed last February.

It remains unclear whether the Supreme Court would order refunds directly or leave the matter to lower courts or federal agencies. Trump has also overstated the scale of tariff collections, claiming the US has collected or will soon collect $600 billion. In reality, US Treasury data show that net customs duties reached a record $195 billion in fiscal 2025, which ended on September 30, with monthly collections averaging in the low $30 billion range thereafter.

Market sentiment has shifted against Trump’s chances of prevailing. Online betting platforms Kalshi and Polymarket currently assign him a roughly 30% and 23% probability of success, respectively, down from about 40% before the court hearings, reflecting the justices’ apparent scepticism, according to Reuters.

With multiple rulings imminent and others on the horizon, the Supreme Court is entering a period that could redefine the balance of power between the presidency, Congress and the courts, while also shaping US economic and social policy for years to come, Reuters reported.

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