What do you think "legitimate" means?
There have been some supreme court rulings and some amendments on this. I'm not terribly up to date. A pretty good reading of some insights can be found here:
https://www.aclu.org/technology-and-liberty/testimony-legislative-counsel-gregory-nojeim-know-your-customer-banking-regulI quote:
The Supreme Court ruled in United States v. Miller, 425 U.S. 435 (1976) that individuals do not have a "reasonable expectation of privacy" under the Fourth Amendment in financial records pertaining to them but maintained by a bank in the normal course of business.
As a consequence the right to financial privacy act was created:
http://en.wikipedia.org/wiki/Right_to_Financial_Privacy_ActBut that was amended later, including by the patriot act. It's a pretty complex legal issue with lots of back n forth. As it stands though, there simply isn't a big debate about the constitutional backing of monitoring people or even citizens. There is huge political consensus between republicans and democrats of the value of things like the patriot act, KYC/AML, the patriot act and generally any anti-terrorist act, many of the things the democrats chided republicans for during the Bush years have essentially been copied and extended to the extent that Cheney was praising him for it, and KYC/AML is probably the least controversial part of that package. Most people simply don't care because they don't think they'll ever be affected. (e.g. I'll never launder money in my life, what do I care?). But philosophically and politically this is a very dangerous way of thinking even though it makes a lot of sense intuitively.
It's one of the most disappointing things of the past decade in my opinion, because Obama ran for a big part on his ability to showcase constitutional infringements by his predecessor. After all, he taught constitutional law at an ivy league plus university, after having been educated to do so at an ivy league university. If you look at past interviews he has a very strong constitutional understanding, but has sadly completely waved it away. The most ironic one being:
http://floppingaces.net/wp-content/uploads/2011/04/verbatim_obama-copy.jpg which is something he said while running for president in response to Bush's policies, obviously repeating the exact same mistake shortly after.
Glenn Greenwald did a nice presentation on this at Brown some time ago you can see here:
https://www.youtube.com/watch?v=ikCUHh3Ge_kYou could contact the EFF to see if they have any info on this. Again I'm not terribly up to date.