A majority of Supreme Court justices seemed sceptical on Wednesday about US President Donald Trump's ability to unilaterally impose far-reaching tariffs, putting at risk a cornerstone of his agenda in the biggest legal test yet of his unprecedented presidency.

Three conservative justices raised questions about whether an emergency law gives Trump near-limitless power to set and change duties on imports, with potentially trillion-dollar implications for the global economy.

The court's three liberal justices also appeared dubious, so at least two conservative votes could limit Trump's tariff power, though likely not end it altogether.

The case is the first major piece of Trump's agenda to come squarely before the nation's highest court, which he helped shape by naming three of the nine ju

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