Portions of the search warrant that was used to search Congressman Jefferson's office were recently struck down as unconstitutional by a federal appeals court:

The FBI violated the Constitution when agents raided U.S. Rep. William Jefferson's office last year and viewed legislative documents, a federal appeals court ruled Friday.

The court ordered the Justice Department to return any privileged documents it seized from the Louisiana Democrat's office on Capitol Hill. The court did not order the return of all the documents seized in the raid.
...
The U.S. Court of Appeals for the District of Columbia Circuit rejected that claim. The three-judge panel unanimously ruled that the search itself was constitutional but that FBI agents crossed the line when they viewed every record in the office without giving Jefferson the chance to argue that some documents involved legislative business.

"The review of the Congressman's paper files when the search was executed exposed legislative material to the Executive" and violated the Constitution, the court wrote. "The Congressman is entitled to the return of documents that the court determines to be privileged."

In other words, an arm of the executive branch (the FBI) was not allowed to go after privileged information belonging to the legislative branch.  So I'm assuming then that the opposite must then be true as well... and that the legislative branch does not have the authority to subpoena privileged records of the executive?

Thoughts anyone?