Refusal to deal (also known as a group boycott) is one of several anti-competitive practices forbidden in countries which have restricted market economies. For example:
Agreements involving competitors that involve restricting the supply of goods are prohibited if they have the purpose or effect of substantially lessening competition in a market in which the businesses operate.
—Australian Competition & Consumer Commission, Refusal to deal 
"Refusal to deal" includes any agreement which restricts, or is likely to restrict, by any method the persons or classes of persons to whom goods are sold or from whom goods are bought