The EU is poised to launch one of its biggest trade cases against China in a generation after telling member states it has compiled firm evidence that Beijing’s telecommunications equipment companies have benefited from illegal state subsidies.

The commission has been piecing together the case for months, according to several officials and executives briefed on the case, focusing on the activities of two Chinese makers of mobile network equipment, Huawei and ZTE.

EU officials informed representatives from the bloc’s 27 member states at a closed-door meeting on Thursday they believed the commission had “very solid evidence” that those companies benefited from illegal government subsidies and had sold products in the EU below cost, a practice known as “dumping”.