The Concentrated Phosphate Export Association consists of the five largest phosphate producers. The Agency for International Development (AID) undertook to sell fertilizer to Korea and solicited bids. The association set prices and submitted a single bid on 300,000 tons. A paid the contract price, determined the amounts to be purchased, coordinated the procedure for buying, and undertook to resell to Korea. The Justice Department sued the association and its members, claiming that their actions violated Section 1 of the Sherman Act. What defense might the defendants have? What is the result?