Facebook Inc CEO Mark Zuckerberg has been forced more and more to defend his Internet.org initiative against accusations of violating net neutrality, and now a coalition of 65 advocacy organizations from 31 countries have sent an open letter to the Facebook founder, calling for changes to be made to the Internet.org platform.

“We, the undersigned, share a common concern about the launch and expansion of Facebook’s Internet.org platform and its implications for the open Internet around the world,” the letter says. “On that open Internet, all content, applications and services are treated equally, without any discrimination. We are especially concerned that access for impoverished people is construed as justification for violations of net neutrality.”

Zuckerberg responded to criticisms of Internet.org earlier this month by announcing that the platform would be opened up to developers to create new applications for the service. The Facebook CEO dismissed claims that he should adhere more strictly to net neutrality principles, and he hinted that detractors “put the intellectual purity of technology above people’s needs.”

Facebook is “building a walled garden”

The coalition of Internet.org critics argue that while the service has admirable goals, it does more harm than good.

“It is our belief that Facebook is improperly defining net neutrality in public statements and building a walled garden in which the world’s poorest people will only be able to access a limited set of insecure websites and services,” the letter states.

“Further, we are deeply concerned that Internet.org has been misleadingly marketed as providing access to the full Internet, when in fact it only provides access to a limited number of Internet-connected services that are approved by Facebook and local ISPs. In its present conception, Internet.org thereby violates the principles of net neutrality, threatening freedom of expression, equality of opportunity, security, privacy and innovation.”

Whether or not Internet.org actually markets itself as “the full Internet,” a survey by LIRNEasia earlier this year found that a number of people in several Southeast Asian countries responded that they used Facebook but not the internet.

The main sticking point for many net neutrality supporters seems to be Internet.org’s zero rate agreements with local ISPs, which provide certain services for free at the exclusion of others.

“This practice is inherently discriminatory,” the letter states, “which is why it has been banned or restricted in countries such as Canada, the Netherlands, Slovenia and Chile.”