There is more subtlety in this case. The NSA has interpreted the law in a specific way which justifies their activities. If the Supreme Court later determines t

There is more subtlety in this case. The NSA has interpreted the law in a specific way which justifies their activities. If the Supreme Court later determines that interpretation is invalid, they most definitely can be convicted of a crime. If the Supreme Court instead determines that their interpretation of the law was valid, but that the law itself was unconstitutional, then ex post facto protection would apply.