President Donald Trump on Saturday said he would increase global tariffs to 15% from 10%, one day after the Supreme Court struck down his “reciprocal” tariffs.

The new tariffs will be “effective immediately,” Trump said in a Truth Social post.

“I, as President of the United States of America, will be, effective immediately, raising the 10% Worldwide Tariff on Countries, many of which have been “ripping” the U.S. off for decades, without retribution (until I came along!), to the fully allowed, and legally tested, 15% level,” he wrote.

In his social media post Saturday, Trump also warned that additional tariffs would follow.

“During the next short number of months, the Trump Administration will determine and issue the new and legally permissible Tariffs,” he wrote.

The White House did not immediately respond to a CNBC request for comment.

The increase comes after the Supreme Court on Friday, in a 6-3 tariff ruling, decided that Trump wrongfully invoked the International Emergency Economic Powers Act (IEEPA) to implement his levies.

Trump responded the same day with a 10% global tariff, exercising his authority under Section 122 of the Trade Act of 1974. The statute allows the president to implement only temporary levies, with any extension requiring congressional approval.

The president was scathing in his remarks against the Supreme Court decision, calling it in his social media post that it was “ridiculous, poorly written, and extraordinarily anti-American.”

He also attacked Justices Neil Gorsuch and Amy Coney Barrett after they voted with the majority in the ruling.

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U.S. trading partners offered a cautious welcome to the U.S. Supreme Court’s decision Friday to strike down large parts of President Donald Trump’s flagship trade policy on global tariffs — but global trade bodies warned of lingering uncertainty surrounding import levies.

The law that undergirds the import duties “does not authorize the President to impose tariffs,” the majority ruled six to three in the long-awaited Supreme Court decision.

Hours after the ruling, Trump said he signed an executive order imposing a new 10% “global tariff”. The “Section 122” tariffs will take effect “almost immediately,” Trump said. At a White House press briefing Friday afternoon, Trump railed against the “deeply disappointing” 6-3 ruling.

Trump’s tariff regime impacted a swathe of countries from the U.K. to India and the European Union. Some governments, like Vietnam and Brazil are still in negotiations.

Taiwan, home to the the world’s leading contract chipmaker and producer of the most advanced semiconductors, said the 10% flat tariff rate would, according to an initial assessment, have a “limited impact” on its economy.

The island will continue to “closely monitor” developments and maintain close communication with the U.S. to understand the specific measures and respond in a timely manner, the Taiwanese cabinet said in a statement on Saturday.

French President Emmanuel Macron reportedly said the Supreme Court’s ruling proved the benefit of having an effective counterweight to power.

“It is not bad to have a Supreme Court and, therefore, the rule of law,” Reuters quoted him as saying at an event in Paris on Saturday.

A U.K. government spokesperson said the country would continue to work with the White House administration to understand how the ruling will affect tariffs for the U.K. and the rest of the world

“This is a matter for the U.S. to determine but we will continue to support U.K. businesses as further details are announced,” the spokesperson said.

“The U.K. enjoys the lowest reciprocal tariffs globally, and under any scenario we expect our privileged trading position with the U.S. to continue.” The U.K. agreed a wide-ranging trade deal with the U.S. in May last year, which imposed a broad 10% levy on many goods, but also included certain carve-outs on steel, aluminum, cars and pharmaceuticals.

The Supreme Court case focused mainly on reciprocal tariffs, and the ruling leaves much of the U.K.’s trade deal with the U.S. — including preferential sectoral tariffs on steel, pharmaceuticals and autos — unaffected.

However, the British Chambers of Commerce (BCC) trade body said the U.S. Supreme Court decision adds to the ongoing uncertainty around levies.

William Bain, head of trade policy at the BCC, said the move “does little to clear the murky waters” for British businesses, warning that the President still has “other options at his disposal” to retain his current regime on steel and aluminum tariffs.  

“The court’s decision also raises questions on how U.S. importers can reclaim levies already paid and whether U.K. exporters can also receive a share of any rebate depending on commercial trading terms,” Bain said in a statement. “For the U.K., the priority remains bringing tariffs down wherever possible.”

Olof Gill, European Commission spokesperson for trade and economic security, said businesses on both sides of the Atlantic depend on “stability and predictability.”

“We remain in close contact with the U.S. Administration as we seek clarity on the steps they intend to take in response to this ruling,” Gill said. “We therefore continue to advocate for low tariffs and to work towards reducing them.”

Meanwhile, Dominic LeBlanc, Canada’s minister for U.S.-Canadian trade relations, said the decision “reinforces Canada’s position that the IEEPA tariffs imposed by the United States are unjustified.”

The prospect of a U.S. attack on Iran has roiled oil prices this year, but analysts tell CNBC a strike would require more military commitment and be more complicated, than the U.S. is prepared for.

Tensions are high, and despite talks last week in Oman, both sides remain at an impasse. U.S. President Donald Trump’s pressure on the Iranian regime escalated after a brutal crackdown on anti-government protestors across the country last month.

Trump said this week he was considering sending a second aircraft carrier to the Middle East, even as Washington and Tehran prepare to resume talks. On Tuesday, he threatened Iran with “something very tough,” if it does not agree to Washington’s demands, which range from halting the country’s nuclear enrichment to cutting Tehran’s ballistic missile program.

The U.S. deployed the USS Abraham Lincoln carrier strike group to the Middle East in January. This brought the number of missile destroyers in the region to six, but, analysts say, this still wouldn’t be enough to topple the regime. Following through on his “something tough” threat would mean a prolonged conflict in a region Trump is wary of.

“U.S. forces in the region are not adequate to support a significant long-term military operation in Iran which would be necessary to achieve any major military objective,” Alireza Ahmadi, executive fellow at the Geneva Center for Security Policy, told CNBC.

Trump has also dialed up his pressure on the Islamic Republic, applying financial pressure to an economy already crippled by sanctions. Just last month, he vowed to impose tariffs on any country that acquires any goods or services from Iran.

But it is unclear what could come next. “President Trump is notoriously unpredictable,” Ali Vaez, director of Iran Project at Crisis Group, told CNBC but added Trump is aware “the Iran problem set does not lend itself to clean and easy military options.”

The White House claimed after strikes on three main nuclear sites last year that Iran’s nuclear facilities were “obliterated.” Iran moved to quickly repair the damage to ballistic missile sites but according to analysis from the New York Times, has made “limited fixes” to the major nuclear sites hit by the United States.

Iran has long claimed it does not have any plans to develop nuclear weapons. As talks restart between Washington and Tehran, Iran has offered to cap its enrichment at low levels. The U.S. has opposed the Iranians enriching any uranium since the nuclear deal collapsed in 2018.

While the U.S. has vowed to attack Iran if it resumes its nuclear and missile programs, it is unclear whether these sites would again be primed for attack. “Both options are likely to lead to a disproportionate Iranian retaliation, which could then turn the confrontation into a regional conflagration,” Vaez said.

Shares of Sweden’s Volvo Cars tumbled as much as 19% on Thursday morning, putting the company on track for its worst trading day ever.

The automaker, which is owned by China’s Geely Holding, posted a substantial drop in fourth-quarter operating profit, citing the impact of U.S. tariffs, negative currency effects and weak demand.

Volvo Cars said fourth-quarter operating income excluding items affecting comparability fell by 68% to 1.8 billion Swedish krona ($200.46 million) compared to the same period a year prior.

“We have a very challenging market, especially in China, very tough competition. All of our European colleagues have the same problem,” Volvo Cars CEO Hakan Samuelsson told CNBC’s “Europe Early Edition” on Thursday.

He added the discontinuation of EV incentives in the U.S. and China were also contributing to “a very challenging external environment.”

“But internally we have had very good work done with lowering our costs and securing a positive cash flow, so that I would highlight as the most important positive things that we have reached during the year,” he added.

Shares of Volvo Cars were last seen down 18.1%, having pared some of its earlier losses. A single-session fall of more than 11.2% would reflect the firm’s worst trading day ever.

The U.S. and EU agreed to a framework trade deal in July last year, one which saw the Trump administration impose a blanket tariff of 15% on most EU goods, a significant reduction from Trump’s threat of 30% and almost halving the tariff rate on Europe’s auto sector from 27.5%.