Source : Webster's Revised Unabridged Dictionary (1913)

Ultra vires \Ul`tra vi"res\, [Law Latin, from L. prep. ultra
   beyond + vires, pl. of. vis strength.]
   Beyond power; transcending authority; -- a phrase used
   frequently in relation to acts or enactments by corporations
   in excess of their chartered or statutory rights.

Source : WordNet®

ultra vires
     adj : beyond the legal power or authority of a person or official
           or body etc; "an ultra vires contract" [ant: {intra
           vires}]
     adv : beyond the scope or in excess of legal power or authority