In a letter to uSocial, Facebook said the company was breaking several laws including illegally accessing the site.
However uSocial, which announced in September this year that it was planning to sell friends on the social network, claimed it was doing nothing wrong.
"We have been dealing with Facebook regarding this matter and we have removed our friend-buying service, though we're not budging on selling fans," said uSocial CEO Leon Hill.
We are well within our legal right to do so and despite the C&D, we're not taking the service down."
However, despite Facebook's issue with the company, uSocial said it would continue its service.
"We're actually not too worried by this and we'll be ramping up our Facebook services in the coming weeks," said Hill.
"We'll shortly be launching a similar service with Facebook groups, though we will have to wait and see what the response is from that."
See also: uSocial to sell Twitter followers