A senior EC official has criticised hi-tech firms for helping China silence its domestic critics.
Wallstroem: Firms must remember their responsibilities
In a blog entry, EC vice president Margot Wallstroem said Microsoft, Yahoo and Google were matching their morals to suit new markets.
In particular she said the firms seemed to have deleted words such as "ethics" and "corporate social responsibility" from their codes of conduct.
She urged the companies to re-discover their responsibilities.
Ms Wallstroem wrote her comments after learning about the lengths Microsoft, Yahoo and Google have gone to in order to accommodate the wishes of the Chinese government.
Google is reportedly amending its index to exclude information to which the Chinese government objects. Microsoft and Yahoo have also submitted to the demands of Chinese authorities.
In her blog, Ms Wallstroem wrote that the firms "have flexible ethical standards depending on where they operate".
She went on to say that the companies needed to realise that active support of democracy and corporate responsibility was necessary for growth. She urged the companies to read the UN Global Compact which stresses the need for uniting business goals and human rights.
Comments left by readers on her blog said the EC too should examine its record on relations with China.
In September Yahoo was accused by Reporters Without Borders of providing information that helped Chinese authorities link journalist Shi Tao with e-mails that allegedly divulged "state secrets".
Mr Tao was subsequently jailed for 10 years for sending the messages.
At the time Yahoo said it had to operate within the laws of each country in which it traded.
In June 2005 it emerged that Chinese users of Microsoft's net services writing blogs are having censored some journal entries mentioning "freedom", "democracy" and "demonstration".
Pop-up warnings asked writers to use another expression for these terms which were banned.
Microsoft too said it had to respect local laws.
The Chinese economy is exploding and it is increasingly becoming an attractive new place for both on and offline firms to do business.
For media and net based companies setting up a business in China, this also means adhering to local rules, including tight state controls of the press and restrictions governing what websites can say.