As an FYI- if by "worried about an increase" you mean an escalation in the $200 fee it cant happen.
The original 1936 NFA which set the fee is somehow written in such a way that the $200 fee is inextricably linked with the NFA. To increase it would require a repeal of the NFA laws and then a re-draft of them- which would leave a "Wild West" window open for a fairly long time.
COngress tried back in the 1960's to increase the fee to, iirc, $500 but failed do to the nature of how the original NFA is written. Remember, when the law was first written one could get a Thompson mailed to you from Sears with 100 rnds of ammo and 2 drums for $50- so a $200 tax per weapon seemed like a GREAT way to keep guns out of the hands of most people.
So the actual NFA fee cannot be raised. Now- I'm not sure if they can tack on additional fees at some point but the $200 NFA Tax stamp is inviolate for purposes of raising it without abandoning the NFA for a rewrite (and the way our laws are done is before a new law can replace the old one the old one needs to be repealed)
AN interesting side note- do you know why corporations are exempt from the tax? Thank Henry Ford. Ford had the largest private army under arms in America at the time (his fabled strike breakers). Ford had, literally, a few hundred or more full-auto weapons and did not feel like paying a few hundred thousand in tax stamps for them. SO he used his influence to get the NFA amended to exempt corporations from the tax since the guns would be owned by the corp and not an individual.
ANother intersting point re: the head of Treasury. The head of Treasury, according to the NFA, may declare an amnesty at any time without Congressional or Presidential approval in order to put Class 3 weapons back in order (the only time this has happened was of course in 1968).
