Mark Zuckerberg, chief executive officer and founder of Facebook Inc. attends the Viva Tech start-up and technology gathering at Parc des Expositions Porte de Versailles on May 24, 2018 in Paris, France.

Internal Facebook documents have been seized by the British parliament in an aggressive move that will likely set the tone for a high-stakes hearing due to take place this week.

Damian Collins, chair of the U.K.'s Digital, Culture, Media and Sport Committee (DCMS), used a rare parliamentary power to compel Ted Kramer, the founder of app-maker Six4Three, to hand over the documents during a business trip to London, The Observer newspaper reported late Saturday.

The files are reported to contain confidential emails in relation to Facebook's data and privacy controls in the run-up to the firm's data scandal earlier this year. It has also been reported that the cache of documents contains emailed correspondence with Facebook Chief Executive Mark Zuckerberg and other senior executives.

The news comes as Facebook readies itself for a crucial hearing before the DCMS committee in London on Tuesday, which is set to be attended by Richard Allan, the company's vice president of policy solutions, as well as political officials from Canada, Ireland, Latvia and Singapore. Zuckerberg snubbed the committee several times when asked to appear and provide evidence.

According to multiple media reports, the procedure to obtain the documents was attended by the serjeant at arms, an official responsible for maintaining order in the House of Commons, the lower chamber of the U.K. parliament.

Collins confirmed that the committee had obtained the documents from Six4Three. "I have reviewed them and the committee will discuss how we will proceed early next week," he wrote via Twitter.

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Now-defunct U.S. firm Six4Three, which developed an app called Pikinis that let people pay to find pictures of users in swimsuits, is currently engaged in a legal battle with Facebook. The Pikinis app was shut down in 2015 after Facebook changed its policies around the sharing of user data with third-party app developers. Six4Three argues Facebook drove developers away through anti-competitive means.

The internal documents seized by U.K. lawmakers relate to the lawsuit, and were reportedly obtained by Kramer's lawyers through the legal discovery process.

"Six4Three's claims are entirely meritless — Facebook has never traded Facebook data for anything and we've always made clear that developer access is subject to both our policies and what info people choose to share," a Facebook spokesperson told CNBC in an email.

"We operate in a fiercely competitive market in which people connect and share. For every service offered on Facebook and our family of apps, you can find at least three or four competing services with hundreds of millions, if not billions, of users."