Federal law stipulates that one who purchases a suppressor must pay a $200 "transfer tax" to the BATF, and obtain a tax stamp from them. Failure to pay the tax is punishable by a (IIRC) $10,000 fine and a 10 year prison sentence.
This law is unconstitutional on its face (infringement, anyone?), and any court not corrupted by leftist ideology would reject it as such.