We have laws regarding this practice. As a practice, it's not forbidden, but agencies must show cause to secret courts which have a remarkable record for speedy response without leaks. These courts were set up so that law enforcement would have some oversight and so civil liberties of American citizens would have some protections even in extenuating circumstances.

Not only were these courts not consulted, but a number of lawyers who worked for the Executive branch (many of them Republican appointees) found the practice objectionable and corrosive. Congress, which made the law, was not consulted on the subject of changing the law.

Now that it's out in the open, the Administration claims it can do whatever it wants in wartime. However, unlike ancient Rome, we have no mechanism for giving a leader dictatorial (and I use this in the Roman sense) powers. Besides which, I personally have trouble with giving an Administration untrammelled spying abilities which claims "executive privilege" in an investigation of its own response to the Katrina debacle. It sounds to me like they simply want to do whatever they want without answering to anybody. Uh uh.