"I commend Google for coming to the conclusion that cooperating with the 'Great Firewall' of China is inconsistent with their human-rights responsibilities," Durbin said. "Google sets a strong example in standing up to the Chinese government's continued failure to respect the fundamental human rights of free expression and privacy. I look forward to learning more about whether other American companies are willing to follow Google's lead."
The letters ask the companies for details about their Chinese operations and what, if any, measures will be put in place to prevent human-rights abuses by the country's government.
Durbin is following up on a letter he sent to a wide range of tech firms last year, asking them to join a voluntary code of conduct known as the Global Network Initiative, which has been backed by Google, Microsoft and Yahoo.
Some companies, including Twitter and Toshiba, did not respond to last year's letter. In 2008, Durbin held a hearing during which he questioned Google, Yahoo and Cisco about their human-rights practices.