Banking unprivavcy is a complete violation of the 4th amendment. The argument is that you are voluntarily giving your information to this third part.
1. It is not voluntary. You need to bank to exist in society.
2. It is federal law that these banks have to invade your privacy in this way. They are mandating that these third parties spy on you. It is a dirty loophole.
If you don't have the evidence to get a warrant, maybe you shouldn't be spying.