WordNet (r) 3.0 (2006):

power structure
    n 1: the organization of people at different ranks in an
         administrative body [syn: hierarchy, power structure,
         pecking order]

Moby Thesaurus II by Grady Ward, 1.0:

133 Moby Thesaurus words for "power structure":
   amperage, animal kingdom, aristocracy, armipotence, authority,
   barons, beef, black power, brute force, bureaucracy, caste,
   chain of being, charge, charisma, class, class structure, clout,
   cogence, cogency, compulsion, condition, cream, dint, directorate,
   domain, drive, duress, echelon, effect, effectiveness,
   effectuality, elite, energy, establishment, flower power, footing,
   force, force majeure, forcefulness, full blast, full force,
   hierarchy, higher echelons, higher-ups, influence, kingdom,
   lords of creation, main force, main strength, mana, management,
   might, might and main, mightiness, mineral kingdom, ministry,
   moxie, muscle power, natural hierarchy, nobility, officialdom,
   order, overlapping, pecking order, pizzazz, place, poop, position,
   potence, potency, potentiality, power, power elite, power pack,
   power struggle, powerfulness, precedence, prelacy, prepotency,
   productiveness, productivity, puissance, pull, punch, push,
   pyramid, rank, rate, rating, realm, ruling circles, ruling class,
   ruling classes, sinew, sphere, stage, standing, station, status,
   steam, strength, strong arm, superiority, superpower,
   the Establishment, the administration, the authorities, the best,
   the best people, the brass, the ingroup, the interests,
   the people upstairs, the power elite, the power structure, the top,
   them, they, top brass, top people, upper class, upper crust,
   validity, vegetable kingdom, vehemence, vigor, vim, virility,
   virtue, virulence, vitality, wattage, weight