Taiwanese prosecutors on Tuesday charged a former lieutenant colonel and his father with spying for China in the latest allegations of espionage on the island.
The men are accused of threatening national security by sharing information and recruiting others in exchange for gifts, the Tainan district prosecutor's office said.
The younger man, identified by local media as Cheng Chih-wen, helped recruit Taiwanese soldiers "to develop networks to seriously affect national security and damage military discipline", prosecutors said in a statement.
His father Cheng Chao-ming, who heads a small political party, introduced his son to Chinese agents in Japan in 2009 while he was still in service, prosecutors said.
The son then allegedly signed an agreement pledging to help China's attempts to incorporate the self-ruled territory at a Singapore meeting in 2010, when he received $11,000 and a Tissot watch.
After he was discharged from the military, the younger Cheng introduced a former colleague to Chinese agents while on overseas trips, receiving more money in return.
Taiwan and China have spied on each other since 1949, when nationalist troops fled to the island and set up a separate government after losing a civil war on the mainland to communist forces.
Beijing is deeply suspicious of President Tsai Ing-wen's traditionally pro-independence Democratic Progressive Party and has cut off official communication with Taipei since she came to power in 2016 over her refusal to accept that the island is part of "one China".
Pressure is building up again as Taiwan gears up for new elections in January, with Tsai seeking a second term against a challenger who favours warmer ties with China.
The case comes after two directors of Hong Kong-based China Innovation Investment Limited were stopped from leaving Taiwan last month. They are currently being investigated on suspicion of violating national security laws.
The company said they were being probed over sensational claims made by Chinese defector Wang "William" Liqiang that he was recruited by the directors to conduct spy-ops in Hong Kong, Taiwan and Australia.
China, however, has accused 26-year-old Wang of being an unemployed fraudster and fugitive.