Looks like OSHA is forwarding some legislation to place safety controls on the shipment of explosives and small arms ammo, which I imagine includes blackpowder and caps. Although I'm not certain what that does as far as blackpowder sales, it merits a look-see. Many reenactors are up in arms, as well as other organizations who advocate shooting.
The docket number is OSHA-2007-0032 and you can look this up on the Federal Regulations site and decide for yourself if this is a real threat to the hobby.
If anything, be proactive and write your Congressman and tell him what you think. Just don't start your letter/email with "Dear Miserable Little Worm".