Coca-Cola and PepsiCo are under preliminary investigation at the Federal Trade Commission over potential price discrimination in the soft drink market as the agency looks to revive a decades-old but largely dormant law banning the practice. The companies’ pricing strategies are being scrutinized under a law known as the Robinson-Patman Act. The law prohibits suppliers from offering better prices to large retailers at the expense of their smaller competitors. The largely dormant 1936 law is aimed at promoting a level playing field between small retailers and large chain stores.