Details over at The Captain's Journal.
Herschel is correct: the reporting demand has no basis in federal law. In addition, it would seem to be an end run around the prohibition on spending federal dollars compiling a registry of guns and/or gun owners, but the courts upheld it anyway. Twice.
This will send the message that executive federal agencies can create policy from whole cloth -- policy that has no authority in law, yet is as enforceable as if it does -- and the courts will back them up.
And it's likely that, before much longer, it won't be just the southern border states.