Specifically, the 4th amendment, to the US constitution protecting US citizens against unreasonable search and seizures. Normally this would involve anything searched or seized without warrant.
Where the federal government goes to a court and requests some case for the search or seizure of specific information. Anything that deviates from these requests and the specific information they obtain warrants for is forbidden and against the law. So anyone that is involved in any of the warrant-less surveillance of US citizens either directly or indirectly should be thrown in jail.
So this procedure has been shown to be exact opposite of what the NSA and FBI have been doing. They have been collecting information under blanket approvals issued by some secret kangaroo court and then using parallel construction to establish some kind of case against those that get caught up in the net.