See the U.S. Constitutional analysis of FATCA article Neill has found.
From the document:
“…The FATCA reporting requirements arguably resemble that of a general search warrant. It was enacted in order to curb tax evasion of U.S. citizens using foreign accounts.
However, while the information reported can be useful to the IRS in confirming the income reported by individuals, there are no particularized suspicions in collecting this information from every foreign U.S. account.
Doing so assumes that every U.S. citizen with a foreign account is a “crook” evading his taxes.201
Additionally, the searches at hand contain the potential for abuse. This is due to the “access to this information without invocation of the judicial process.”202
The scrutiny of a neutral magistrate helps to balance societal and individual interests in the collection of the information at hand.203
Without a warrant issued through the judicial process, the search is an unreasonable violation of the individual account holders’ Fourth Amendment rights…”