Yes exactly, what Adam said. Unless there is a contractual obligation, such as working for a creative staffing agency, who charges the client say, $130 / hr for your work and pays you $70. But that is completely different. Is there some explicit arrangement where someone in the company is demanding X percentage from you for the referrals? It's a bit unclear from your original post. But I think that would be a bit unorthodox and not a little shady. If you did the work, on your machines, it's your money. They shouldn't demand a "finder's fee" from you, and even if it's their client, they don't have the facilities to provide what you can do. They don't own the client. The hope is, the client is happy with their recommendation and gives them more work in the future.
That being said, most folks I know love a nice bottle of bourbon or scotch. Just saying.
-TG