By Donie O'Sullivan and Hadas Gold, CNN

(CNN) -- Mark Zuckerberg and his colleagues were apparently concerned enough about Vine, a video app from Twitter, that on the day it launched in January 2013, they moved to restrict its access to Facebook user data, a trove of internal Facebook emails released by the U.K. Parliament on Tuesday shows.

The decision to restrict Vine's access to data, which would have allowed its users to invite their Facebook friends to join the app, was in line with a company policy at the time, Facebook told CNN on Tuesday. That policy restricted apps' access to Facebook data when the company deemed that the apps "replicated" Facebook's "core functionality." In other word, apps that Facebook thought might compete with them.

"Twitter launched Vine today which lets you shoot multiple short video segments to make one single, 6-second video," Facebook vice-president Justin Osofsky wrote to Zuckerberg and others the day Vine launched, according to the emails released by the UK Parliament.

"Unless anyone raises objections, we will shut down their friends API access today. We've prepared reactive PR," Osofsky added.

"Yup, go for it," Zuckerberg responded.

Facebook said Tuesday that Zuckerberg and his colleagues were only following Facebook's policy protecting against competitors. But the company changed the policy on Monday, one day before the emails were released.

"As part of our ongoing review we have decided that we will remove this out of date policy so that our platform remains as open as possible. We think this is the right thing to do as platforms and technology develop and grow," a Facebook spokesperson said Tuesday.

"We built our developer platform years ago to pave the way for innovation in social apps and services. At that time we made the decision to restrict apps built on top of our platform that replicated our core functionality," the spokesperson said, adding, "These kind of restrictions are common across the tech industry with different platforms having their own variant including YouTube, Twitter, Snap and Apple."

Vine, which allowed users to shoot and posts six second looped videos, shut down in 2017. Twitter did not immediately respond to a request for comment.

Apparently responding to Tuesday's revelations, Vine co-founder Rus Yusupov tweeted, "Competition sucks, right? No. It allows for products to improve, become available to more people, at lower costs. Strive to build new things that people want and influence other creators for the cycle to continue."

The documents

The email discussion about Vine is part of a trove of internal Facebook documents the company fought to keep secret.

The documents include conversations among senior Facebook executives as well as emails with outside app companies.

The cache stems from a lawsuit brought against Facebook by a small app company called Six4Three. A California judge had placed the documents under seal. But when the app company's CEO, Ted Kramer, was in London last month, he was escorted to Parliament and told to produce the documents or be held in contempt.

Six4Three — which had an app that allowed users to search for pictures of their friends in swimsuits — has accused the social media giant of having little regard for user privacy and claimed that Zuckerberg devised a plan that forced some of Facebook's rivals, or potential rivals, out of business. Facebook says the lawsuit is without merit.

The UK parliamentary committee, led by Damian Collins, asked for the documents as part of a larger investigation into Facebook, fake news, disinformation and data privacy that has been going on for more than a year. The committee has repeatedly asked Zuckerberg to give evidence, but thus far he's avoided the committee, even when it brought together lawmakers from nine different countries for an unprecedented "International Grand Committee on Disinformation."

"I believe there is considerable public interest in releasing these documents. They raise important questions about how Facebook treats users data, their policies for working with app developers, and how they exercise their dominant position in the social media market," Collins said on Twitter. "We don't feel we have had straight answers from Facebook on these important issues, which is why we are releasing the documents."

A Facebook spokesperson said in a statement after the release of the documents, "As we've said many times, the documents Six4Three gathered for their baseless case are only part of the story and are presented in a way that is very misleading without additional context. We stand by the platform changes we made in 2015 to stop a person from sharing their friends' data with developers. Like any business, we had many of internal conversations about the various ways we could build a sustainable business model for our platform. But the facts are clear: we've never sold people's data."