Eight Taiwanese, due to have been deported home from Kenya, were instead sent to China last Friday after being forced to board a mainland airline - in what Taiwan furiously denounced as an "illegal abduction" orchestrated by China.
In a fast-brewing diplomatic storm, the island yesterday lodged a protest with its neighbour across the Taiwan Strait and demanded the return of its nationals.
Observers believe China's move is yet another attempt to tighten the screws on incoming President Tsai Ing-wen ahead of her May 20 inauguration.
"It is to demonstrate to the world that there is one China - and China is the only representative of that," said Tamkang University analyst Edward Chen I-hsin.
Ms Tsai has not publicly accepted a 1992 consensus - that both sides agree they are part of China even if they differ on what it means. It is endorsed by the current Kuomintang government helmed by President Ma Ying-jeou. Beijing says recognising it is a prerequisite for continuing stable cross-strait ties.
Taiwan's Ministry of Foreign Affairs (Mofa) yesterday said the eight were among 23 Taiwanese nabbed in Kenya for being part of a phone scam.
They were acquitted and were due to be deported home. But Chinese officials forced the Taiwanese to take a China Southern Airlines flight, it said. They also thwarted Taiwan's representative in South Africa from reaching them in time.
Yesterday, a senior Taiwanese official overseeing cross-strait relations, Ms Shih Hui-fen, told legislators the plane landed in Guangzhou in South China but it is unclear where the eight were then taken to.
She added: "This has not only undermined the fundamental human rights (of the eight) but has hurt the feelings of the Taiwanese people and severely affects ties between both sides." In a statement, Mofa called it "an uncivilised act and a trampling on human rights".
It was not the first time Taiwanese had been sent to China. In 2011, the Philippines deported 14 Taiwanese fraud suspects to China. But that incident was likely a case of the Philippines acting unilaterally in adherence to a "one China" policy, said Dr George Tsai of the Chinese Culture University.
The Kenya episode, however, has China's fingerprints all over it, said Dr Chen. "China may want to hold the eight as hostages or bargaining chips in dealing with Ms Tsai."
A spokesman for China's Ministry of Foreign Affairs, asked about the accusations at a routine briefing, claimed he had not heard of the case. When queried again, he said: "I will find out more about it. But as a matter of principle, countries that uphold the one-China policy are worthy of approval."
Ms Tsai and her pro-independence Democratic Progressive Party won the presidential and legislative polls on Jan 16. Since then, Beijing has signalled that it intends to punish the island if Ms Tsai does not uphold the 1992 consensus.
Last month, China broke an implicit diplomatic truce with Taiwan, establishing formal ties with Gambia, a former ally of Taiwan.