(Bloomberg) — Solar imports from Southeast Asia are being unfairly sold in the US below their production costs, according to initial findings of a Commerce Department review that laid out duties of as much as 271% to counteract the practice.

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The preliminary determination released Friday marks another victory for US solar panel makers that argued those cheap imports are harming their business and undermining government investments meant to nurture a domestic supply chain.

At issue are imports of crystalline silicon photovoltaic cells — and modules made with them — from Cambodia, Malaysia, Thailand and Vietnam, countries which provide the bulk of US supply of that equipment today. Those nations provide the bulk of US solar cell and module imports. The announcement comes nearly two months after the US agency issued preliminary findings from a separate but related probe that the solar imports from Southeast Asia are unfairly benefiting from government aid.

The investigations represent the latest bid by US manufacturers to confront overseas rivals. After similar duties were imposed on solar imports from China roughly 12 years ago, Chinese manufacturers responded by setting up operations in other Asian nations that weren’t affected by the tariffs. The US probes were triggered by an April petition from the American Alliance for Solar Manufacturing Trade Committee, which represents companies including First Solar Inc. (FSLR), Hanwha Qcells USA Inc. and Mission Solar Energy LLC.

“With these preliminary duties, we are moving closer to addressing years of harmful unfair trade and protecting billions of dollars of investment in new American solar manufacturing and supply chains,” Tim Brightbill, partner at Wiley Rein and lead counsel to the petitioners, said in an emailed statement. “These initial rates are in line with our expectations of market conditions and how these four countries were engaging in unfair trade practices to undermine American manufacturing and jobs.”

Shares of First Solar rose as much as 3.8% after the announcement, while JinkoSolar’s US depository receipts fell as much as 2.9%.

The cases have drawn opposition from some foreign manufacturers and domestic renewable power developers that argue tariffs give an unfair advantage to larger incumbent panel makers operating in the US while raising the cost of solar power projects.