Plaintiffs, soft drinks retailers, brought suit alleging that their wholesalers had engaged in an unlawful conspiracy to restrain trade by refusing to sell soft drinks unless plaintiffs paid cash in advance or at the time of the delivery. The wholesalers had an agreement that none of them would grant short-term credit although such credit had been extended in the past. Question: Is the agreement a breach of the antitrust laws? Explain briefly the reason behind your answer.