Tate & Lyle has filed a case in the US against three Chinese firms, alleging infringement of its patents covering the sweetener sucralose.
Splenda is an important source of profits for Tate & Lyle
The British sugar and sweetener company said it had filed the case with the US International Trade Commission (ITC).
Tate & Lyle said the US case had also been brought against 18 importers and distributors.
Sucralose, which is also sold under the name Splenda, accounts for about one fifth of Tate & Lyle's profits.
The three Chinese manufacturers named in the case are Hebei Sukerui Science and Technology Co. Ltd, Changzhou Niutang Chemical Plant Co. Ltd and Guangdong Food Industry Institute.
"Our sucralose manufacturing technology is protected by a robust and sophisticated patent estate, which we will defend rigorously," said Robert Gibber, general counsel of Tate & Lyle.
The company said it had filed a similar case in May 2006 which had resulted in favourable settlements with three of the 10 defendants.
In January this year, Tate & Lyle issued a profit warning following weaker-than-expected sales of Splenda.
Sales of the sugar-substitute were hit by declining business in the US carbonated soft drink sector, with consumers increasingly choosing alternatives to fizzy drinks.