Questioning the Supreme Court and other government branches needs to stay within the range of fair criticism or "run the risk in our society of undermining institutions that we need to preserve our liberties," Justice Clarence Thomas said Thursday.

Thomas also told an audience at the University of Florida law school that some comments he hears about the court "border on being irresponsible."

He didn't speak specifically about the court's recent decision on campaign financing or mention President Barack Obama. But Thomas' comments come a week after Obama took the rare step of openly criticizing the decision during his State of the Union speech.

Thomas supported the 5-4 ruling that allows companies and unions to spend freely on ads that promote or target candidates by name.