Vexatious litigation is legal action which is brought, regardless of its merits, solely to harass or subdue an adversary. It may take the form of a primary frivolous lawsuit or may be the repetitive, burdensome, and unwarranted filing of meritless motions in a matter which is otherwise a meritorious cause of action. Filing vexatious litigation is considered an abuse of the judicial process and may result in sanctions against the offender.
Italicized emphasis mine.
burdensome? I'd have to ask Yahoo whether the FBI was going to foot the bill for the time spent gathering the information.
unwarranted? as suggested by the literal lack of warrant, check
All that's left is the FBI to try to apply the all writs act and now we've got the litigation portion covered.
Now you'd have Yahoo required and the FBI expressly forbidden from completing the actions by law. I think this needs to see trial.