US specialty materials company Celanese is suing Polish distributor Falken Trade Polska over alleged infringement of its patent on sweetener acesulfame potassium, or Ace-K. The lawsuit, filed in Poland, alleges that the Olsztyn-based firm is selling Ace-K from a Chinese manufacturer that infringes Celanese’s European intellectual property rights.

Celanese had already obtained a preliminary injunction in November, preventing Falken Trade Polska from continuing to sell the sweetener.

The lawsuit follows another that the Texas-based group filed in March against three Chinese manufacturers of Ace-K, namely Suzhou Hope Technology, Anhui Jinhe Industrial and VitaSweet. At that time, Celanese said it had withdrawn its complaint to the US International Trade Commission, attributing the decision to a “temporary shift in focus.” The company has instead requested that the US Patent and Trade Office review additional claims to its patented and improved Ace-K manufacturing process.

China’s custom agency revealed last month that it had detected more than 1,560 cases of intellectual property infringement involving goods exported to the US, noting that the cases stemmed from two joint China-US crackdowns this year.

In August, US President Donald Trump authorized an inquiry into China’s alleged theft of intellectual property, which is estimated to be worth as much as $600 billion. The US Chamber of Commerce said China must end forced technology transfer and protect foreign-owned intellectual property rights.