Taiwan officials in Hong Kong have been told their visas will not be renewed if they don't sign a document supporting Beijing's claim to Taiwan under its "one China" policy, a person with direct knowledge of the matter told Reuters.
The move comes after Taipei strongly criticised a new security law imposed on Hong Kong by Beijing, and opened an office in Taipei this month to help people who may want to leave the Asian financial hub.
Several Taiwanese officials at its de facto Hong Kong consulate who were due to renew their visas have been asked by the city's government to sign the document, a senior Taiwan official with knowledge of the matter told Reuters.
The official said the move was unprecedented and presented an "unnecessary political obstacle" for Taipei-Hong Kong ties.
"They won't issue the visa if we don't sign the document," the official said, declining to be named due to the sensitivity of the matter. "It's entirely a problem created by them."
"We will try our best to defend our stance. Our representatives in Hong Kong will hold fast to their position."
The Hong Kong Immigration Department did not immediately respond to a request for comment.
Taiwan's China policy-making Mainland Affairs Council urged Hong Kong to return to "existing consensus" to maintain normal exchanges between Taiwan and Hong Kong.
"Hong Kong should follow mutual agreements to ensure the office is free from political interference, and should not establish unnecessary obstacles beyond those agreements," it said in a statement to Reuters.
Taiwan has 15 Taiwanese staff at its de facto consulate in the city, another person with knowledge of the matter said.
China sees Taiwan as part of "one China" and has never renounced the use of force to bring the island under its control.
China has proposed that Taiwan be brought under Chinese rule under a similar "one country two systems" arrangement it offered to Hong Kong. Taiwan President Tsai Ing-wen rejects the proposal, which she calls a "failure".
The source declined to say exactly how many Taiwan officials were asked to sign the paper but said its acting chief, Kao Ming-tsun, had returned to the island late on Thursday after he refused to sign the document upon his visa renewal.
Reuters was not immediately able to reach Kao for comment.
Kao's return to Taiwan due to the political spat was first reported by Taiwan online publication Up Media.
Taiwan announced this week it will enhance scrutiny over investment from Hong Kong to prevent illicit money from mainland China, days after Reuters reported the move.
Hong Kong has long served as an important trade and investment conduit between Taiwan and China, which have no diplomatic relations.
Hong Kong's new security law punishes what China broadly defines as subversion, secession, terrorism and collusion with foreign forces with up to life in prison.
Critics of the law fear it will crush the wide-ranging freedoms promised to the former British colony when it returned to Chinese rule in 1997, while supporters say it will bring stability to the city after a year of sometimes violent anti-government protests.