Facebook, YouTube, Twitter and Microsoft Sign Hate Speech Agreement

FORTUNE — Some of the biggest U.S. tech firms have signed up to a code of conduct formulated by the European Commission, in which they agree to help fight against the spread of hate speech in Europe.

Online rights groups have reacted with outrage, saying they have no confidence in the agreement because they were left out of the discussions leading up to it (a point now being investigated by an EU watchdog) and they think the deal fails to protect free speech rights.

Facebook, YouTube,  Twitter  and Microsoft  MSFT promised to review most reports of illegal hate speech on their platforms within 24 hours and act on them by removing or disabling access to the content, as long as the complaints are precise and substantiated. Their terms of service and community guidelines will have to be clear that they prohibit hateful conduct and incitements to violence.

Based on a 2008 piece of legislation, the code of conduct describes the illegal material as “all conduct publicly inciting to violence or hatred directed against a group of persons or a member of such a group defined by reference to race, color, religion, descent or national or ethnic origin.”

According to a statement, the companies recognize that illegal hate speech has a negative impact not only on individuals, but also on “those who speak out for freedom, tolerance and non-discrimination in our open societies and has a chilling effect on the democratic discourse on online platforms.”