FILE PHOTO: Hong Kong Chief Executive Carrie Lam attends a thematic forum of the second Belt and Road Forum for international cooperation in Beijing, China, April 25, 2019. REUTERS/Jason Lee

HONG KONG (Reuters) - The European Union Office in Chinese-ruled Hong Kong issued a formal diplomatic “demarche” protest note to Hong Kong’s leader on Friday over a proposed extradition law that could see individuals sent back to mainland China for trial.

The proposed legislation has stoked mass protests in the former British colony, which was promised a high degree of autonomy, including an independent judiciary, under a “one country, two systems” formula when it returned to China in 1997.

Critics, including foreign governments, legal and business groups, have expressed fears the law could erode Hong Kong’s rule of law and leave individuals, including foreign nationals passing through the city, vulnerable to being sent back for an unfair trial on the mainland.

The EU Office in Hong Kong and Macau said in a brief statement in response to press inquiries that it had, together with diplomatic representatives from its member states, met with Hong Kong’s leader Carrie Lam to “carry out a demarche reiterating their concerns regarding the government’s proposed amendments to Hong Kong’s Fugitive Offenders Ordinance”.

The 28-member European Union had already come out in recent months to express concern over the extradition bill that Hong Kong authorities say they want to try to get passed in the city’s legislature before the summer recess.

This latest move represents a hardening of the EU position, just days after Lam reiterated that she wouldn’t scrap the bill.

The head of the EU office, Carmen Cano, wasn’t immediately available for comment. There was no immediate comment from Lam’s office.