The warning from the U.S. and its four closest intellignce partners follows several arrests of U.S. service members for allegedly trying to pass info to China.

The U.S. and its intelligence partners warned on Wednesday that China is working to recruit current and former Western military pilots and other service members to help strengthen Chinese air power and gain insights into Western aviation tactics.

Describing China’s efforts as a “persistent” threat, the warning came in a joint bulletin from the so-called Five Eyes intelligence partners, five nations that share sensitive intelligence: the U.S., the United Kingdom, Canada, Australia and New Zealand.

China’s People’s Liberation Army (PLA) “is using private companies in South Africa and China to hire former fighter pilots from Canada, France, Germany, the United Kingdom, Australia, the United States, and other Western nations to train PLA Air Force and Navy aviators,” the bulletin said.

“The PLA wants the skills and expertise of these individuals to make its own military air operations more capable while gaining insight into Western air tactics, techniques, and procedures. The insight the PLA gains from Western military talent threatens the safety of the targeted recruits, their fellow service members, and U.S. and allied security.