Authorities in the Chinese capital are building sentry posts in the suburbs, with police and community volunteers on the lookout for "three kinds of people," ahead of key political anniversaries.
A source close to the campaign, identified only by his surname, Li, said security measures are being tightened ahead of the 22nd anniversary of the military crackdown on the student-led pro-democracy Tiananmen Square protests of 1989.
Checkpoints will be manned around the clock by police, he said.
"Basically, it is petitioners they are looking for, along with Falun Gong practitioners, and anyone whose children died in the June 4 crackdown."
The authorities are also keen that planned celebrations of the 90th anniversary of the founding of the Chinese Communist Party shouldn't be marred by public displays of protest against its rule.
"They are building a sentry post at the main intersection in every village," Li said. "There will be a big gate and a rampart, so when the gates are closed, they will keep petitioners out and stop them from spoiling July 1."
Security 'stepped up'
Li said the structures would be in place from mid-May to mid-July.
"They will be manned together by Beijing municipal police and village security guards, who will be checking anyone coming in from outside," he said.
Beijing-based rights activist Hu Guang said security would also be stepped up in the city center ahead of June 4, with police clearing the capital of any ordinary Chinese pursuing complaints against government officials.
"Usually they will send them back to the provinces, or put them under surveillance," Hu said. "I heard that around 200 people have already been detained."
"Beijing petitioners Li Xuehui, Yang Qiuyu, and Li Xiaocheng from elsewhere in China, and Feng Xixia ... some of them have been sentenced to labor camp," he added.
"I have to go to the police station myself, twice every Monday, to 'chat' with them."
Barred from Beijing
Local governments have also been strengthening measures in recent months to block petitioners from traveling to Beijing to air their grievances, activists say.
In Shanghai, authorities have distributed notices around the city warning petitioners not to travel to Beijing at risk of being detained or sent to a labor camp.
Petitioners have reported seeing notices in recent weeks threatening detention for a first-time violation and labor camp for a second, and claiming that petitioning in Beijing is a crime, although the notices bore no official seal.
Sichuan-based rights activist Liu Feiyue, who founded the group Civil Rights and Livelihood Watch, said he had been following the case of hundreds of contract teachers from the northern province of Hebei as they planned to travel to Beijing to complain about their pay and conditions.
"The news got out because there were a few phone calls going back and forth between the teachers," Liu said.
"Some of the teachers were held in their own homes, while others were followed by [police], so they can't leave home to go to the station."
Migrant workers warned
Thousands of petitioners go to Beijing each year to seek redress for complaints against their local governments.
They are frequently held in "black jails," which stand outside the criminal justice system, and are escorted back to their hometowns by local governments, which run representative offices in the capital for the purpose.
Meanwhile, authorities in the southern city of Shenzhen issued a notice on a government website, warning migrant workers in the city that they were banned from launching petitions in the event of their wages being unpaid.
"It is strictly forbidden for migrant workers to use mass-petitioning, or other informal means, as a way of demanding their wages," the notice, signed by the Shenzhen municipal residential construction bureau, said.
It also forbade employers hiring migrant workers to withhold their pay, for any reason.
"Anything causing serious consequences or exerting an evil influence will be pursued according to the law," it warned.
'A long history'
Petitioning authorities for redress has a long history in China, and the Shenzhen directive was quickly slammed by the official People's Daily newspaper.
"It doesn't matter how reasonable the intentions," said a signed opinion article on Monday. "The price for them cannot be the sacrifice of the legal rights and interests of a group of people."
Shortly after the article was published, the Shenzhen government retracted its directive, official media reported.
The current system, set up five decades ago to serve as a bridge between the ruling Communist Party and the people, seldom resolves problems, instead sparking detentions, beatings, and harassment of those who dare to complain, according to petitioners and social activists.
The contemporary "letters and visits" system was formally established in 1951 and reinstated during the 1980s following the large number of appeals against summary verdicts handed down during the political turmoil of the Cultural Revolution (1966-76).
China says it receives between 3 million and 4 million complaints in the form of "letters and visits" annually, with the number having peaked at 12.72 million in 2003.
Reported by Qiao Long and Fang Yuan for RFA's Mandarin service. Translated and written in English by Luisetta Mudie.