@Peladon Re: Actually, No
How about a cursory reading of the US Constitution?
The US Congress does in fact posses the ability to create new courts and funnel certain types of cases to those courts. That's essentially what they did with this law.
Furthermore, the claim of damages is specious at best. Given the way the law is written, the letters in question are going to third parties, not the targets of the investigations. As third parties who are essentially being asked to testify against the target, they are unlikely to have protections against self-incrimination. On the other hand, revealing even the existence of such a letter can clearly undermine the work of collecting information to apprehend and prosecute the subject.
Whether or not such policies are wise for a democratic republic is certainly a good question. And I would feel better if there were a more rigorous court reviewing the requests. However, they are quite constitutional.