Washington. President Donald Trump on Monday imposed a 25 percent tariff on goods imported from Japan and South Korea, while setting new import taxes on a dozen other nations that will take effect on Aug. 1.

Trump announced the move by posting letters on Truth Social addressed to the leaders of the affected countries, warning them against retaliating with higher import taxes or facing further tariff hikes.

“If for any reason you decide to raise your tariffs, then whatever the number you choose to raise them by will be added onto the 25% that we charge,” Trump wrote in letters to Japanese Prime Minister Shigeru Ishiba and South Korean President Lee Jae Myung.

The letters, more a declaration than a negotiation, reflect Trump’s willingness to escalate trade disputes as he seeks to bolster domestic manufacturing and fund tax cuts signed into law last Friday. While Trump insists the tariffs are necessary to strengthen the US economy, economists warn they risk slowing growth and increasing the likelihood of a recession.

“It’s all done,” Trump told reporters Monday. “I told you we’ll make some deals, but for the most part, we’re going to send a letter.”

South Korea’s Trade Ministry said Tuesday it would accelerate negotiations with the United States to reach a deal before the tariffs take effect.

The tariffs will hit imports from Myanmar and Laos at 40 percent, Cambodia and Thailand at 36 percent, Serbia and Bangladesh at 35 percent, Indonesia at 32 percent, South Africa and Bosnia and Herzegovina at 30 percent, and Kazakhstan, Malaysia, and Tunisia at 25 percent.

Trump inserted the word “only” before the rates in his letters, implying generosity. However, the letters followed a standard format, with one sent to Bosnia and Herzegovina initially addressing its female leader, Željka Cvijanović, as “Mr. President.” Trump later posted a corrected version.

White House press secretary Karoline Leavitt said the president is crafting “tailor-made trade plans for each and every country,” adding that the administration will continue posting the letters on social media before mailing formal copies, a break from the traditional closed-door negotiations used by previous administrations.

Trade experts expressed concern over the tariff hikes. Wendy Cutler, vice president at the Asia Society Policy Institute and a former US trade official, called the moves “unfortunate,” saying Japan and South Korea are close economic and security partners with the US, particularly in shipbuilding, semiconductors, and critical minerals.

Trump’s trade challenges extend beyond Asia. Talks with the European Union and India remain unresolved, while imports from China are already taxed at 55 percent. South African President Cyril Ramaphosa’s office said the announced tariffs mischaracterized its trade relationship with the US but affirmed its commitment to pursuing a “balanced and mutually beneficial” agreement.

Markets reacted to the announcement, with the S&P 500 falling 0.8 percent Monday and yields on 10-year Treasury notes climbing to nearly 4.39 percent, potentially raising mortgage and auto loan rates.

Trump declared an economic emergency to impose the tariffs, citing trade deficits as justification. While Congress typically controls tariff policies, the president can use emergency powers, though the authority is under legal challenge. The administration is appealing a May court ruling that found Trump exceeded his authority.

The strategic logic of targeting Japan and South Korea --key regional partners in countering China-- is unclear. “These tariffs may be modified, upward or downward, depending on our relationship with your country,” Trump wrote.

The tariffs take effect in three weeks, allowing for last-minute negotiations. Scott Lincicome, a vice president at the Cato Institute, said, “I don’t see a huge escalation or a walk back, it’s just more of the same.”

The administration had initially imposed lower baseline tariffs during a 90-day negotiation period, which ends Wednesday. Trump signed an executive order Monday delaying the tariff increases until Aug. 1, effectively extending talks.

Trump’s team promised 90 trade deals in 90 days but has secured only two frameworks so far, including one with Vietnam to deter China from routing goods through that country and another with the UK to ease tariffs on steel, aluminum, and autos.

According to the Census Bureau, the US ran a $69.4 billion trade deficit with Japan and a $66 billion deficit with South Korea in 2024. Under Trump’s letters, autos will face a 25 percent tariff globally, while steel and aluminum imports will be taxed at 50 percent.

The tariffs mark a return to Trump’s combative trade tactics. During his first term, the Trump administration renegotiated trade agreements with Japan and South Korea, which it then touted as victories for U.S. farmers and manufacturers.

Trump has also threatened additional tariffs on countries aligned with BRICS, including Indonesia, which would face further 10 percent levies.