People suspected of drunken driving can't automatically be subjected to blood tests without a warrant and without their consent, the U.S. Supreme Court has held.
Justice Sonia Sotomayor wrote the majority opinion (PDF) in Missouri v. McNeely. The natural metabolization of alcohol does not justify an automatic exception to the Fourth Amendment's warrant requirement, Sotomayor wrote. Instead, the need for a warrant “must be determined case by case based on the totality of the circumstances,” she said.
Source ABA Journal