Former Democratic Progressive Party (DPP) worker and human rights activist Lee Ming-cheh is being held by Chinese police at an undisclosed location, his wife said on Tuesday.
"I received indirect evidence from a government department late last night that Lee Ming-cheh has been detained by a branch of the state security police," Lee's wife Lee Ching-yu told reporters in Taipei.
"I am extremely concerned about whether or not Lee Ming-cheh has food and money while in detention," she told a news conference.
"I hope that the Chinese government will apply the standards of a civilized country and tell us on what charges Lee Ming-cheh is being detained or arrested, and also to allow his family members to visit him," Lee Ching-yu said.
Lee, a Taiwan community college manager and lifelong member of the island's ruling DPP, had been incommunicado since arriving in mainland China from Macau to seek medical advice for a sick relative on March 19.
Lee, 42, was reportedly on his way to visit a doctor with his mother-in-law’s medical records when he "disappeared" after he crossed the internal immigration border into Zhuhai city, in the southern province of Guangdong.
A friend who had planned to meet him said he never showed up, according to media reports at the time.
Interest in human rights
Lee is employed by Taipei Wenshan District Community College but used to work for the DPP and had a long-running interest in human rights issues in China.
His wife says she is worried that he will have run out of necessary medications.
"He just had a regular amount of medication for high blood-pressure with him, which won't be enough," she said.
"I am planning to hand over his blood-pressure medication and some money to the Straits Exchange Foundation today," she said.
Taiwan's Straits Exchange Foundation (SEF), a semi-official body charged with managing ties with mainland China in the absence of formal diplomatic links, said it has "indirect evidence" that Lee has been detained by a law enforcement agency of the Chinese government.
The SEF had made inquiries about Lee's status after a request from his wife, who didn't specify which "government department" had told her about the information.
A clear signal
Yang Sen-hong, who heads the Taiwan Association for China Human Rights, said Lee's detention sends a clear signal that there is a huge gulf between democratic Taiwan and the ruling Chinese Communist Party regime when it comes to human rights and the rule of law.
He said a worsening climate for human rights under the administration of President Xi Jinping means that many people have no idea when their activities will be treated as crimes.
"This is different, and everyone feels insecure," Yang said. "Nobody knows when the day might come when they get detained, and if so, on what charges."
"That's how it goes in China: they detain you, and then they ponder at their leisure [what to do with you]," he said. "Of course they are saying it's to do with national security, but that won't be accepted in Taiwan."
He said the case could put a further strain on cross-straits ties, which have cooled since the DPP's landslide election victory in January 2016.
Taiwan's Presidential Office said the government is doing all it can via its official Mainland Affairs Council (MAC) to help secure Lee's release.
Held under new law?
Some activists have expressed concern that Lee may be being held under China's recently enacted Overseas NGOs Domestic Activities Management Law, which enables police to engage in daily supervision and monitoring of foreign civil society and rights groups operating in China.
The legislation hands full authority for the registration and supervision of foreign NGOs in China to the country's ministry of public security, and police across the country.
They have the power to cancel any activities, revoke an organization's registration, and impose administrative detention on its workers, as well as take part in the annual assessment of foreign NGOs required for the renewal their operating permit.
Police can also blacklist NGOs deemed guilty of national security-related crimes like subversion or separatism, although definitions of such crimes remain vague.
The DPP once campaigned on a pro-independence platform, and while the party's rhetoric has softened in recent years, President Tsai Ing-wen has stopped short of endorsing a 1992 agreement with the Chinese Communist Party signed by her predecessors in the nationalist Kuomintang (KMT), angering Beijing.
Taiwan began a transition to democracy following the death of President Chiang Ching-kuo, in January 1988, starting with direct elections to the legislature in the early 1990s and culminating in the first direct election of the island's president, Lee Teng-hui, in 1996.
Recent opinion polls indicate that there is broad political support for de facto self-rule in Taiwan, where the majority of voters identify as Taiwanese rather than Chinese.
But while the Chinese Communist Party has never ruled the island, Beijing regards it as part of Chinese territory and has threatened to invade if Taiwan seeks formal independence.
Reported by Ng Yik-tung and Sing Man for RFA's Cantonese Service. Translated and edited by Luisetta Mudie.