U.S. Congress and human rights watchdogs criticize the world’s leading internet service companies for helping the Chinese government censor "sensitive" internet contents.

The New York-based group Human Rights in China (HRIC) revealed that many "sensitive" search results are blocked by the newly launched Google.cn- a Chinese-based version of Google search engine -to prevent them reaching Chinese Internet users, according to a statement from HRIC.

Some examples of filtered or censored search queries include "Human rights in china" in Chinese, "Rights defenders" in Chinese, "Chinese Communist Party" in Chinese, "Tiananmen Square" and among others. It is worth to note that by using the Chinese interface of Google.com or Google.com.tw for the same search queries yielded diverse results as Google.com.

"Google joins a host of other leading technology companies, including Microsoft and Yahoo, who have bowed to Chinese government demands in attempts to gain ground among the growing Chinese online population," HRIC lamented, adding that such concessions "would curtail freedom of expression and access to information in China."

Not only the political freedom of Chinese citizens is jeopardized by the censorship, religious freedom has also become another concern for religious materials on the internet may also be blocked from the believers in China.

An evangelical Christian group Focus on the Family quoted the comments from the U.S.-based Chinese Christian persecution watchdog China Aid Association (CAA) on the issue. The chairman Bob Fu said Chinese Christians were among the internet savvy. Among 100 million internet users in China, many of them are Christians who depend on the internet for spiritual food, he said.

"Christians are forming internet chatting rooms do discuss the gospel, their church. It’s been increasingly influential to the ministry of the gospel in China," he added. The list of censored words includes Christian "God" and "Christ."

Meanwhile, the Congressional Human Rights Caucus headed by House Congressman Tim Ryan (D-Oh) is holding hearings to investigate Google, Microsoft, and Yahoo! for collaborating with China to censor the internet. All three companies have declined to appear before the Congressional Human Rights Caucus on Wednesday for the briefing. The companies were condemned for allowing profits to precede democratic values such as freedom of speech, sources say.

The companies have been summoned to a Feb. 15 hearing by the House International Relations Subcommittee, which oversees human rights issues.

Microsoft and Yahoo did release a joint statement calling on the US government to help solve censorship problems in China.

"We urge the United States government to take a leadership role in this regard and have initiated a dialogue with relevant US officials to encourage such government-to-government engagement," the statement said.

Anti-censorship groups, Reporters Without Borders, Amnesty International and Human Rights Watch want Congress to introduce a uniform code of conduct to protect freedom of speech.