By Michael Bristow
BBC News, Beijing
China's economy has liberalised, but its political system has not
Chinese lawyers, dissidents and academics who signed a document calling for political reform are being harassed by the authorities.
Signatories to the Charter 08 document have been detained, questioned by the police and put under pressure at work.
The charter calls for a radical overhaul of China's political system by introducing elections, a new constitution and an independent judiciary.
Despite 30 years of economic reforms, China's political system has hardly changed in that time.
And the authorities' reaction to this latest call for reform suggests the country's leaders still have no appetite for political reforms.
Charter 08 was published last month on the 60th anniversary of the promulgation of the Universal Declaration of Human Rights.
December also marked three decades since China began reforms that have transformed the economy and the country's fortunes.
But even before the document was published, the police started visiting some of the 300 or so original signatories.
Writer and dissident Liu Xiaobo is believed to be under a form of house arrest at an undisclosed location in Beijing.
Freedom to assemble
The authorities have yet to state publicly why the 53-year-old has been detained.
He is believed to be the only signatory being held by the police, but others have experienced other kinds of harassment.
Police went to journalist Li Datong's work unit to look for him. He was not there, but now he knows the authorities are watching him.
Shanghai lawyer Zheng Enchong has been taken in for questioning four times since the document was published.
Li Boguang, another lawyer, was invited to meet with a Chinese security official at a Beijing coffee shop, where for more than an hour he had to explain why he had added his name to the charter.
"The official didn't say anything. He just listened to my reason and then left. This is how they operate," he said.
China usually metes out severe treatment to anyone who criticises the system, but Mr Li said he still thinks it was right to sign the charter.
"Change requires ordinary citizens, particularly intellectuals, to speak out. This will slowly influence the government," he said.
Another signatory, academic Xu Youyu, experienced a different kind of pressure.
Mr Xu, a professor at the Chinese Academy of Social Sciences, was told by his boss that signing the document broke Chinese laws.
"I told him that was nonsense. That's absolutely not the case," the expert in Western philosophy told the BBC.
He was then asked to retract his signature, which he refused to do. "I am willing to pay any price for this," he added - even going to prison.
Liu Xiaobo is in detention at an undisclosed location
Mr Xu has also been told that he will not now be allowed to write the foreword to the book of a colleague.
"The publishers received an order from the centre saying that everybody who signed their name to the charter had lost their qualification to publish any article or any book," he said.
The document that appears to be causing so much concern among senior Chinese leaders is one of the most important published in several years.
It was based on Charter 77, which in 1977 called for respect for human and civil rights in what was then Czechoslovakia.
Charter 08 says the Chinese government's approach to modernisation has been "disastrous".
It "deprives humans of their rights, corrodes human nature, and destroys human dignity," the document says.
It calls for a political system that guarantees human rights, freedom of expression and protection for private property.
It has also stirred interest abroad. Several Nobel laureates, among others, have written to Chinese President Hu Jintao asking him to release Liu Xiaobo.
China's leaders are saying little about Charter 08 - or the detention of Mr Liu.
But President Hu made it clear in a speech to mark the 30th anniversary of the country's reforms that China would not adopt Western-style democracy.
Willy Lam, of the Chinese University of Hong Kong, said China's leaders are nervous about calls for political change.
This nervousness has increased with the country's economic problems, which could create a restless population receptive to calls for political change.
Mr Liu's detention is a case of "killing the chicken to scare the monkey", according to Mr Lam.
This is a Chinese idiom that suggests making an example of one person to keep others in line.