The US set new duties as high as 3,521 percent on solar imports from four Southeast Asian countries, delivering a win for domestic manufacturers while intensifying headwinds already threatening the country’s renewable power development.

The duties announced Monday are the culmination of a yearlong trade probe that found solar manufacturers in Cambodia, Vietnam, Malaysia and Thailand were unfairly benefiting from government subsidies and selling exports to the US at rates lower than the cost of production. The investigation was sought by domestic solar manufacturers and initiated under former President Joe Biden.

While the duties are set to benefit domestic manufacturers, they also will pinch US renewable developers that have long relied on inexpensive foreign supplies, heightening uncertainty for a sector whipsawed by political and policy changes in Washington.

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The levies will be in addition to new widespread tariffs imposed by US President Donald Trump that have upended global supply chains and markets. The antidumping and countervailing duties, as they are known, are designed to offset the value of alleged unfair subsidization and pricing, as calculated by the Commerce Department.

The department’s determination is a victory for domestic manufacturing that both Trump and Biden have tried to galvanize. Potential beneficiaries include Hanwha Q Cells and First Solar Inc, among others.

Although the promise of subsidies and demand stoked by Biden’s Inflation Reduction Act have helped drive a wave of interest — and investment — in new domestic solar panel factories across the US, manufacturers warned those factories were imperiled by foreign rivals selling their equipment at below-market prices.

“This is a decisive victory for American manufacturing,” said Tim Brightbill, co-chair of Wiley’s international trade practice and lead counsel for the coalition of solar companies that pursued the case.

Countrywide duties were set as high as 3,521 percent for Cambodia, reflecting the country’s decision to stop participating in the investigation, according to the Commerce Department.

The US imported $12.9 billion in solar equipment last year from the four countries that would be subject to the new duties, according to BloombergNEF. That represents about 77 percent of total module imports.

Companies not named in Vietnam face duties of as much as 395.9 percent with Thailand set at 375.2 percent. Country-wide rates for Malaysia were posted at 34.4 percent. Jinko Solar was assessed duties of about 245 percent for exports from Vietnam and 40 percent for exports from Malaysia. Trina Solar in Thailand faces levies of 375 percent and more than 200 percent from Vietnam. JA Solar modules from Vietnam could be assessed at about 120 percent.

“We don’t think the higher rates will have much financial impact especially post recent reciprocal tariffs,” according to a note by BofA Global Research.

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Indonesia is expected to have more than 20 gigawatts of foreign-owned solar manufacturing capacity by the middle of this year, from just 1 gigawatt at the end of 2022, according to BloombergNEF.

However, other nations including India, Indonesia and Laos could be targeted by a possible new round of duties later this year, according to a note by Roth Industries citing Joseph C Johnson, an associate director at Clean Energy Associates.

The duties hinge on separate action by the US International Trade Commission, which is set to decide in about a month whether producers are being harmed or are threatened by the imports.