Constitutionally (which wasn't explicitly your question, but implied), 4A balancing of considerations that probably requires at least probable cause and most likely a warrant, or exigent circumstances.
Is the drone someplace it has the right to be, doing something it has the right to do, and what are the expectation of privacy in that area... that kind of thing.
Kinda OT, but to clarify, expectation of privacy standard is if you are inside, you have privacy. If you are on the street in plain sight you do not. If you are in your yard surrounded by a privacy fence, you have an expectation of privacy. So sitting in your backyard and your neighbor decides to photograph you over the top of the fence from their 2nd story window or roof, or in this case, their drone, your privacy is being violated.
Allegedly
True. I know how it works. I saw Blue Thunder.