WordNet (r) 3.0 (2006):

restraint of trade
    n 1: any act that tends to prevent free competition in business

Moby Thesaurus II by Grady Ward, 1.0:

56 Moby Thesaurus words for "restraint of trade":
   arrest, arrestation, balance of trade, big business, business,
   business dealings, check, commerce, commercial affairs,
   commercial relations, constraint, control, cooling, cooling down,
   cooling off, curb, curtailment, dealing, dealings, deceleration,
   fair trade, free trade, hindrance, industry, inhibition,
   injunction, intercourse, interdict, legal restraint, market,
   marketing, mercantile business, merchantry, monopoly,
   multilateral trade, prohibition, protection, protectionism,
   protective tariff, rationing, reciprocal trade, rein, restraint,
   retardation, retrenchment, self-control, slowing down,
   small business, tariff wall, the business world, the marketplace,
   thought control, trade, traffic, truck, unilateral trade