President Donald Trump's tariffs are heading to the Supreme Court.
The highest court in the US will decide whether many of Trump's sweeping global tariffs are an illegal overreach of his use of emergency powers as president.
A hearing is scheduled for 5 November.
The court's decision to fast-track the case came after a federal appeals court ruled that Trump's so-called reciprocal tariffs - imposed on nearly every country the US trades with - are illegal
Many of the tariffs that would be affected by the ruling stem from an April announcement at the White House of a flat 10% rate on imports from all countries, which Trump said would even out "unfair" trade relations with the US.
Here's what the court battle over the tariffs could mean for the president's flagship policy.
What did the lower courts say?
Before the case landed at the Supreme Court, two lower courts found that Trump did not have the authority to impose global tariffs.
A late August decision by the US Court of Appeals backed a ruling in May from the Court of International Trade, which rejected Trump's argument that his global tariffs were permitted under an emergency economic powers act.
Trump earlier this year used the International Emergency Economic Powers Act (IEEPA) to declare that large trade deficits with other countries had led to a national emergency. The way to end the deficits and the emergency, he said, was a broad and deep set of tariffs.
The 7-4 decision by the appellate court rejected Trump's argument that the tariffs were permitted under the act, calling the levies invalid.
The judges said the law did not grant "the power to impose tariffs, duties, or the like, or the power to tax".
Trump immediately criticised the judgement, calling the appeals court "highly partisan" and the ruling a "disaster" for the country.
"If allowed to stand, this Decision would literally destroy the United States of America," he wrote on Truth Social.
The case stems from a series of legal challenges over the reciprocal tariffs, including two from small businesses in the US and one brought by a group of 12 US states.
- What tariffs has Trump announced and why?
- US shipping chaos: I fear my wedding sari is destroyed
- US farmers are being squeezed - and it's testing their deep loyalty to Trump
What is the IEEPA?
The decades-old act, which has repeatedly been deployed by Trump during both his terms in office, grants a US president significant authority to respond to a national emergency or a major threat from overseas.
The 1977 law states that a president can pull a number of economic levers "to deal with any unusual and extraordinary threat, which has its source in whole or substantial part outside the United States, to the national security, foreign policy or economy".
It's been used by both Presidents Barack Obama and Joe Biden, who invoked the act to impose sanctions on Russia after the illegal annexation of Crimea in 2014, and then again after the full-scale invasion of Ukraine eight years later.
But the August appeals court stated in its decision that the emergency law "did not give the president wide-ranging authority to impose tariffs".
The IEEPA "neither mentions tariffs (or any of its synonyms) nor has procedural safeguards that contain clear limits on the president's power to impose tariffs", the justices said.
Trump argued when he unveiled his global tariffs that a trade imbalance was harmful to US national security, and was therefore a national emergency.
But the court ruled that the power to impose tariffs, which are taxes on imports, does not belong to the president under the US constitution.
"The power of the purse (including the power to tax) belongs to Congress," the court decided.
Why is the Supreme Court case important?
Beyond being a significant setback to a centrepiece of Trump's agenda, any decision by the Supreme Court that would throw out the tariffs could have an immediate impact on the US economy, with knock-on effects felt in global markets.
Tariffs are taxes that companies have to pay for importing certain goods from foreign countries - so they can have an affect on sales and profit margins.
Historically, tariffs have been aimed at deterring domestic firms from buying foreign goods, in turn affecting international trade.
If the Supreme Court agrees with the lower courts, financial markets could be hit with the one thing traders and banks abhor most - uncertainty.
There will be questions over whether the US will have to pay back billions of dollars that have been gathered by import taxes on products.
It could also throw into question whether major economies - including the UK, Japan and South Korea - are locked into the individual trade deals they secured with the US ahead of the August deadline. Other trade deals currently being negotiated could also be thrown into chaos.
The Supreme Court ruling, whatever it is, will affect Trump's political authority and reputation as a dealmaker. A ruling against him would be a tremendous blow, while one agreeing with him could act as license for even greater changes to how the US trades with other countries.
There are also significant ramifications that could be felt within the political sphere.
For instance, if the Supreme Court reverses the federal appeals court decision and sides with the Trump administration, it could set a precedent that emboldens the president to use the IEEPA more aggressively than he has done so far.
What happens next?
While it's unclear when the top court will issue its decision, both sides have asked for a quick ruling.
The conservative majority on the Supreme Court has frequently sided with him this year.
Six of the nine justices were appointed by Republican presidents, including three who Trump selected during his first term in the White House.
But the court has also been more critical of presidents when it seems they're overreaching on policies not directly authorised by Congress.
During Joe Biden's presidency, for example, the court expanded on what it called the "major questions doctrine" to invalidate Democratic efforts to use existing laws to limit greenhouse gas emissions by power plants and to forgive student loan debt for millions of Americans.
Are there still tariffs in place?
This ruling only affects Trump's "reciprocal tariffs", which includes a patchwork of different rates on most countries around the world, including taxes slapped on products from China, Mexico and Canada.
Those levies on nearly all goods from nearly every country with which the US conducts trade remain in place for now.
Separately, the tariffs Trump has placed under a different presidential authority - known as Section 232 tariffs aimed at protecting US national security - remain intact and unaffected by the court's ruling.
These include sectoral tariffs on steel, aluminium and copper, and recently imposed tariffs on lumber, kitchen cabinets and vanities.
The Trump administration appears more willing to use this authority to impose tariffs and has launched a number of Section 232 investigations, which look at the effect of imports on the national security, including into products like commercial aircraft and jet engines and wind turbines.
