A cache of internal Facebook documents released by a U.K. member of Parliament show how CEO Mark Zuckerberg and other executives wrestled with how to monetize their valuable user data while still encouraging third-party apps to post user activity on Facebook.

In a 2012 email, Zuckerberg suggested making Facebook login and posting content on the platform free while charging “a lot of money” to read user data, like friend information, from the network. App developers would be able to pay the costs directly or offset them with other transactions, like ad buys or use of Facebook’s payment platform, he suggested. That proposal was never implemented, according to Facebook.

Executives also seemed concerned that simply enabling Facebook logins and data access for potentially competing platforms could ultimately cannibalize user activity on Facebook itself.

“Sometimes the best way to enable people to share something is to have a developer build a special purpose app or network for that type of content and to make that app social by having Facebook plug into it,” Zuckerberg wrote in 2012. “However, that may be good for the world but it’s not good for us unless people also share back to Facebook and that content increases the value of our network.”

As Mark Zuckerberg wrote in a Wednesday blog post, the company limited access to data to “prevent abusive apps” starting in 2014. “This change meant that a lot of sketchy apps-like the quiz app that sold data to Cambridge Analytica could no longer operate on our platform,” he wrote.

But the documents also show discussions about giving special friend list access to particular companies, including Airbnb and Netflix, after it was no longer available by default to most developers.

“Facebook have clearly entered into whitelisting agreements with certain companies, which meant that after the platform changes in 2014/15 they maintained full access to friends data,” wrote MP Damian Collins, chair of the Digital, Culture, Media and Sport committee. “It is not clear that there was any user consent for this, nor how Facebook decided which companies should be whitelisted or not.”