The allegation is based on some internal documents that have been published online by a parliamentary committee, with MPs saying that the documents show Facebook had reached secret deals.
Damian Collins, the chair of the committee, wrote on Twitter: "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. (sic)"
However, Facebook has already hit back in the row, saying that "important context" had been omitted from the documents.
A spokeswoman for Facebook explained: "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 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."
Facebook chief executive Mark Zuckerberg has also responded to the issue via a post on the social networking site.
He said: "I understand there is a lot of scrutiny on how we run our systems. That's healthy given the vast number of people who use our services around the world, and it is right that we are constantly asked to explain what we do.
"But it's also important that the coverage of what we do - including the explanation of these internal documents - doesn't misrepresent our actions or motives."