The app developer is suing Facebook over a change to the social network's privacy policies in 2015 that led Six4Three to shut down its app, Pikinis, which let users find photos of their friends in bathing suits by searching their friends list.
According to a new report from the New York Times, internal emails released by a British lawmaker allege that Facebook gave some advertisers and companies special access to data about Facebook users and made decisions about shutting down its competitors' access to data.
"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.
Within the emails are several examples of external companies begging Facebook not to remove user data permissions for their products - perhaps the most prominent victim of which is Twitter and its now-defunct Vine social video app.
Facebook said the documents released Wednesday "are only part of the story and are presented in a way that is very misleading without additional context". "But the facts are clear: We've never sold people's data".
A United Kingdom parliamentary committee has published 250 pages worth of Facebook documents, including emails sent between CEO Mark Zuckerberg and other senior executives.
The documents' publication coincides with a more hawkish shift in public opinion toward online collection of user data, prompted partly by revelations this year of how the political consulting firm Cambridge Analytica misused Facebook users' information.
"Americans' data belongs to them, not Facebook", said Senator Edward Markey, a Massachusetts Democrat. "However, for folks like WeChat, we need to enforce a lot sooner". He also mentioned that Facebook "teams are all really excited about this use case for its potential to (a) have the finserv industry re-think the role of Facebook in retail banking, and (b) act as a test case for more compelling high signal "transactions" over FB messages (sending money, sharing files, customer service with a business, etc.)".
One document said such competitor apps had previously needed Zuckerberg's approval before using tools Facebook makes available to app developers.
"We don't feel we have had straight answers from Facebook on these important issues, which is why we are releasing the documents", said Collins in a Twitter post accompanying the published emails.
Mr Zuckerberg responded: "Yup, go for it".
It suggests that Facebook knew changes that would allow it to collect a record of calls and texts would be controversial on the Android operating system, so made it "as hard of possible for users to know that this was one of the underlying features of the upgrade of their app". The Royal Bank of Canada requested access in one note, as did the dating apps Badoo and Hot or Not.
Facebook also relied on data from Onavo, a company it acquired in 2013, according to the documents. The company limited app developer access to lists of friends, other than those also using the same app, in most cases, according to the statement. The app also sent valuable data on what types of apps people were downloading back to Facebook. "There are a small number of developers whom no amount of sharing to Facebook or monetary value can justify giving them access to Platform".