A business leader from Taiwan has been detained by mainland Chinese authorities and is being investigated over “activities endangering national security”, the mainland’s Taiwan Affairs Office confirmed on Wednesday. Ma Xiaoguang, a spokesman for the office, said Tsai Jin-shu had been under investigation on the mainland since July 2018, without giving further details. Ma said Tsai’s family had been notified and his legitimate rights were being protected. Earlier this month, the Straits Exchange Foundation (SEF) in Taiwan said that Tsai, chairman of the Federation of Southern Taiwan Cross-Strait Associations, had not been seen since July 21, 2018, when he travelled to Xiamen, in the mainland province of Fujian, to attend a food fair. The SEF is a semi-official organisation that liaises with the mainland-based Association for Relations Across the Taiwan Straits on cross-strait issues. On September 13, it said it had sought help through various channels on the mainland to locate 60-year-old Tsai, but there was “no result so far”. The organisation said it had handled 149 cases of Taiwanese who had gone missing on the mainland since May 20, 2016, but had been unable to obtain information in 67 cases. Taiwanese media reported that Tsai had published several commentaries criticising Taiwanese President Tsai Ing-wen and her independence-leaning Democratic Progressive Party. News of Tsai Jin-shu’s detention came days after confirmation that another Taiwanese, Lee meng-chu, was being investigated for engaging in activities that endangered state security. Lee, a volunteer activity organiser from southern Taiwan, was reported to have shared photographs of mainland Chinese troops massing equipment just outside Hong Kong, which has seen months of anti-government protests triggered by a now-abandoned extradition bill . Taiwan’s Mainland Affairs Council called on the mainland to properly handle Lee’s case, while President Tsai said Taiwanese should be cautious when entering the mainland. In March 2017, Taiwanese rights activist Lee Ming-che disappeared while on a visit to the mainland city of Guangzhou, in Guangdong, only to reappear six months later in a court in Changsha, Hunan province. The 44-year-old, who was known to have had discussions about democracy with mainland Chinese on social media, was sentenced to five years in prison. Lee’s wife and mother visited him in a Hunan prison on Tuesday. His wife said she hoped to arrange for Lee to go back to Taiwan for his father’s funeral, but Taiwan Affairs Office spokesman Ma said such an arrangement was against the regulations.