German Defense Minister Boris Pistorius asked China on Saturday to stop recruiting former German Air Force (Luftwaffe) pilots to train Chinese pilots who could help Beijing obtain NATO secrets, AFP reported.

“I raised the issue of German Bundeswehr pilots who were apparently recruited to train Chinese military pilots,” Boris Pistorius told reporters after meeting his Chinese counterpart Li Shanfu Li on the sidelines of a security conference in Singapore.

“I made it clear that I expected an immediate end to this practice and told him that he would probably not be very pleased if I tried to do the same,” the German minister said. According to him, the Chinese minister “did not object, but relativized this issue from his point of view,” Pistorius continued.

German weekly Der Spiegel and German public broadcaster ZDF reported on Friday that several former German military pilots have been recruited by China to train its military pilots in recent years. The German pilots were paid through front companies in the Seychelles, and some of them were allegedly hired by the company of an employee of the Chinese intelligence services.

According to two German media outlets, the business has attracted the attention of the intelligence oversight commission of the Bundestag, Germany’s federal parliament, for several weeks. “We are concerned that these soldiers, while working for the German state, may have a job through which they betray state secrets,” the commission’s president, Konstantin von Notz, told ZDF radio.

The corresponding German pilots were trained on Eurofighter fighters and participated in NATO exercises. Thus, Berlin fears that NATO’s tactical and intervention secrets could have fallen into China’s possession.

The German Ministry of Defense is considering opening an investigation after similar cases were discovered in recent years in the UK and the US