Family and supporters of a Taiwanese man who has been detained in China rallied in Taipei on Tuesday to demand his release, on the eve of a visit by a top Beijing envoy.
Displaying a big wooden cage with a sign reading "Daddy Chung wants to come home", dozens of people urged China to free Chung Ting-pang, a follower of the Falungong spiritual movement allegedly held in China for 51 days.
Chen Yunlin, China's chief negotiator, is due to arrive on Wednesday, Father's Day in Taiwan, to seal a much-awaited investment deal which Taipei has said will provide a legal umbrella for Taiwanese businessmen on the mainland.
"What is the use of Chen's trip and of negotiating an investment pact with China if there is no protection of the personal safety of Taiwanese visiting the mainland?" the protesters said in a statement.
Chung, a technology company manager, was visiting the mainland but has not been seen since he checked in for his return flight on June 18, according to his relatives.
China's state-run Xinhua news agency said in a recent report that Chung, suspected of endangering national security and public safety, had "confessed and shown remorse". Relatives said he might have been forced to confess.
Authorities suspected that Chung obtained classified documents, brought in broadcasting equipment and worked to sabotage television services on the mainland, Xinhua said.
China banned the Falungong in 1999 and strictly prohibits its activities.
Advocates say that the Chung case marks a rare instance in which Beijing has targeted someone not from the mainland.
Taiwanese officials have urged China to release Chung if there is not enough evidence to indict him.