Ericsson’s offices in Beijing were raided by investigators from China’s State Administration for Market Regulation, the Wall Street Journal reported. The company confirmed the probe, and said it follows complaints from unspecified sources about the company’s intellectual property licensing practices.

A Chinese state media report suggested that the investigation is about licensing patents for smartphones. Once 5G-compatible devices are rolled out, handset makers are likely to face an increase in royalty fees they must pay to Ericsson, said the People’s Posts and Telecommunications News. The online report went on to say that Ericsson will likely impose 5G patent fees on top of fees for older generation technologies such as 3G and 4G.

Ericsson said it was cooperating with the investigation.