Authorities in China's central Hubei province are believed to be holding constitutional law scholar Yao Lifa amid gathering momentum for an online campaign to field independent candidates for local parliamentary elections.
Yao, who successfully ran as an independent candidate for the local congress in the late 1990s, hasn't been in contact with friends or family since Monday, his wife said.
"Yao Lifa hasn't come back yet," she said. "He went to work at about noon and didn't come back in the evening."
"We don't know what is actually going on, but I guess he's been taken away by the police or university officials."
Yao's disappearance is thought to be linked to recent announcements by popular microbloggers that they intended to stand as independent candidates in elections to local legislatures.
In 1998, after a 10-year struggle, Yao became the first independent delegate to be elected by winning a municipal seat, but was shunted aside five years later and has been harassed ever since.
The Chinese authorities have warned that there is "no such thing" as an independent candidate, and that anyone hoping to stand for elections this year to the People's Congresses will first have to clear "due legal procedures," the official Xinhua news agency reported.
Apart from a token group of "democratic parties" which never oppose or criticize the ruling Communist Party, opposition political parties are banned in China, and those who set them up are frequently handed lengthy jail terms.
More than two million lawmakers at the county- and township-levels will be elected during nationwide elections, held every five years, in more than 2,000 counties and 30,000 townships from May 7 through December of next year.
Wang Youjin, law professor at the Chinese University of Hong Kong, said that the online campaigners were hoping to use a clause in China's election law which says that candidates not fielded by political parties or other groups must garner the support of 10 or more constituents to get a nomination.
"Those seeking nomination with 10 or more endorsements will still have to get approval from the Communist Party before they can be confirmed as candidates," Wang said.
"You can't nominate yourself if the Communist Party doesn't agree," he said, adding, "In China, policy is law."
One would-be independent, Jiangxi-based laid-off worker Liu Ping, gained the backing of more than 30 people for her nomination in district People's Congress elections, but still didn't make it onto the official list of candidates.
Instead, she was threatened and harassed by the authorities in her hometown of Xinyu city.
Fellow hopeful Li Sihua was also deleted from the list in spite of having the backing of 218 local constituents.
But Li said on Tuesday the campaigners wouldn't give up.
"We are very determined," he said. "We are not concerned about the result of the elections, but about taking part."
"Of course we wouldn't win, and even if we did, we wouldn't be effective as delegates, because we would be suppressed...that's obvious," he said.
"We just...want them to run them according to the rules, according to the Election Law, so that we can take part as [independents]."
Reported by Xin Yu for RFA's Mandarin service. Translated and written in English by Luisetta Mudie.