WASHINGTON -- Since October, the Supreme Court has been 100 percent unanimous in its rulings.

That's probably because the court just issued its first decision in an argued case this term -- a 9-0 opinion written by Chief Justice John Roberts.

The case, OBB Personenverkehr AG v. Sachs , was a quirky one involving the Foreign Sovereign Immunities Act , a law that largely protects foreign countries and their agencies from being dragged into a U.S. federal court.

In an 11-page ruling issued Tuesday, Roberts wrote that OBB, a railway company owned by the Republic of Austria, is shielded from a federal lawsuit brought by a California woman who was horribly injured during a trip abroad.