Please allow me to address the most pertinent point first, before expounding:
Let's begin by taking a look at the definition of the term "infringe:" "to encroach upon in a way that violates law or the rights of another. 'infringe a patent'" - Source Let's take the next step and look at the law which lays the foundation for our right to keep and bear arms: "... the right of the people to keep and bear Arms, shall not be infringed."What's wrong with the ATF requiring dealers to notify them when someone buys more than one firearm in a 24 hour period, and do they have the legal authority to do that?"
Ok, so I'm working this inside out. So what? It makes more sense this way, as that's the way lawyers used to think, anyway. In a nutshell, it says that under a pre-stated condition, there shall be NO impediment (infringement) to a person keeping and bearing arms.
Without any hoopla or doubt whatsoever, the ATF's requirement is infringement. I'm sorry, ATF, but I love my country. I love our Constitution more, and all the laws which stem forth.
I'll never look for a fight, except when someone sets up a punching bag and says "This is the Truth" when it is most certainly not the truth. So, the best approach would be to say "see 'ya!" and disappear until the state find out how much money it lost up its hind end.