As part of the growing backlash to Facebook’s Internet.org project, 65 advocacy organizations from 31 countries released a letter of protest this week to Facebook CEO Mark Zuckerberg. Facebook has partnered with wireless carriers and other organizations on the initiative that hopes to bring free Internet service to the developing world. However, the letter argues that the project “violates the principles of net neutrality, threatening freedom of expression, equality of opportunity, security, privacy, and innovation.”

The project aims to provide developing countries with an app that offers access to certain services, including Facebook, on mobile devices. A group of publishers in India recently pulled out, citing concerns regarding net neutrality.

“To give more people access to the Internet, it is useful to offer some service for free,” Zuckerberg wrote in April in defense of the project. “If someone can’t afford to pay for connectivity, it is always better to have some access than none at all.”

However, there are many who strongly believe such limited access could result in a new digital divide.

“We think that Internet.org exacerbates existing inequalities,” explained Josh Levy of global public advocate Access Now. “The goal here is for poor folks to get limited access to Internet services and then, eventually, be prompted to pay for a data plan so they can get the full Internet. But very likely, a lot of those people will never be able to afford those data plans. So they’ll be stuck on the second tier, where they don’t have access to the full Internet.”

“What’s more, he says, this second tier will undermine security (because it doesn’t used the Internet’s standard SSL security protocol) and privacy (because all traffic is going through a proxy controlled by Facebook),” reports Wired. “Levy argues that Facebook could avoid this split by transforming Internet.org into a service that provides free access to the entire Internet but kept costs down by implementing ‘super low’ data caps.”