The European Union has rebuked China for impinging on Hong Kong’s autonomy over the detention of five men linked to a publishing house and bookshop carrying material critical of Chinese Communist Party leaders, warning that the territory’s status as an international financial hub was at stake.

The owner of Mighty Current Media, Gui Minhai, turned up in the custody of mainland Chinese authorities after going missing in Thailand late last year. After three staffers were also caught in the dragnet while visiting the mainland, manager Lee Bo — who had expressed concern that his boss may have been targeted over an upcoming book about the sex life of Chinese President Xi Jinping — disappeared from Hong Kong, ending up on the mainland apparently without having officially crossed the border.

The men later insisted in televised “confessions” that they had traveled to mainland China voluntarily, but the case has worried Hong Kongers already fearful of encroachment by Beijing, and is seen as an unprecedented breach of the autonomy Hong Kong was promised when Britain handed it over to China in 1997.

In a report to the European Parliament made public Monday, the European Commission and the E.U.’s foreign service said the disappearances “called into serious doubt” the functioning of the principle of “one country, two systems,” under which the Hong Kong Special Administrative Region operates.

Pointing out that two of the booksellers were citizens of E.U. nations — Gui holds a Swedish passport and Lee, also known as Paul Lee, is a British citizen — the report said: “The circumstances of the disappearances were suspicious; the fifth person [Lee] who disappeared from Hong Kong SAR territory seems to have been abducted.”

“The case raises serious concerns about respect for human rights and fundamental freedoms and about the application of [Chinese] criminal law to acts that are not punishable under Hong Kong law,” the report said, calling on Beijing to respect the arrangements for Hong Kong’s autonomy. “The case has potentially lasting implications for Hong Kong’s rule of law and could impact on Hong Kong’s standing as an international business centre.”

Get The Brief. Sign up to receive the top stories you need to know right now. Please enter a valid email address. Sign Up Now Check the box if you do not wish to receive promotional offers via email from TIME. You can unsubscribe at any time. By signing up you are agreeing to our Terms of Use and Privacy Policy . This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply. Thank you! For your security, we've sent a confirmation email to the address you entered. Click the link to confirm your subscription and begin receiving our newsletters. If you don't get the confirmation within 10 minutes, please check your spam folder.

Write to Simon Lewis at simon_daniel.lewis@timeasia.com.