At least one person who helped organize the open letter has been seized by police after its release, according to China Human Rights Defenders, an international network of activists and rights monitoring groups.
"Petitioners like us whose human rights have been abused and are unable to find help, we think: If a country can't even protect basic human rights, then obviously it is not a civilized and modern country," said the letter, addressed to members of the National People's Congress, China's rubber stamp legislature, which convenes next week for its annual session.
"The Olympic Games are supposed to be a competition with civilized rules and civilized people. Countries lacking the spirit of modern civilization do not meet the qualifications to participate," the letter said.
A copy of the letter, written by petitioners seeking redress for alleged government abuses, was posted on the Web site of the Epoch Times, a newspaper banned in China. It was not known whether it was delivered to any Chinese officials.
A growing number of activist groups have sought to leverage China's determination to stage a successful Olympics to shame the host country into changing its policies on human rights, press freedoms and diplomacy. The government has angrily denounced what it calls attempts to "politicize" the games.
One of the letter's organizers, Wang Guilan, was seized by police in Beijing immediately after it was released, China Human Rights Defenders said.
Her whereabouts were unknown, the group said. Wang's cell phone rang busy all day Friday.
Phones at the Beijing Public Security Bureau rang unanswered, and the bureau in Wang's native Hubei province told The Associated Press no one was available to answer questions.
The letter said it was signed by more than 12,700 people, although only five names were provided. Signers included Chinese with grievances over land rights, workers' rights and social security, it said.
The letter called for China to protect human rights guaranteed in the constitution, including freedoms of speech and press, along with the rights to gather, form parties and protest. It also called for Beijing to abolish the power of police to sentence dissidents and petty criminals to labor camps without trial.
Criticism of Beijing has been detracting from its carefully laid plans of using the Olympics to showcase a glittering, dynamic new China.
because he felt China wasn't doing enough to pressure its ally Sudan into ending the humanitarian crisis in its Darfur region.