According to a joint bulletin issued by the US and its closest intelligence allies on Wednesday, China has stepped up its efforts to recruit former Western military pilots and other service members to train its own aviators.

The United States, the United Kingdom, Canada, Australia, and New Zealand—collectively known as the “Five Eyes”—issued the warning.

According to a U.S. official, Chinese military personnel can learn everything from air combat tactics to how to land on an aircraft carrier from Western-trained pilots. Additionally, they may provide China with a valuable glimpse into how to defeat Western military strategies.

Director of U.S. Intelligence Michael Casey stated that China’s People’s Liberation Army has been aggressively recruiting Western military talent to train their aviators to overcome their shortcomings. He added that the operations have been impacted by recent actions by Western governments, but PLA recruitment efforts are evolving in response.

According to the U.S. source, these private corporations have established somewhat autonomous operations in third-world nations like South Africa, Singapore, and Laos. According to this person, Chinese military officials are being trained by former Western pilots, who must be in their dozens or more. These officials then return to China and teach additional pilots there.

The U.S. has attempted to discourage the practice, in part by imposing sanctions on a few of the outside businesses. But according to intelligence officials, China has adjusted.