Horizontal scheme

Four supermarket chains sell seafood in a particular state.  Three of the companies secretly agree to sync up their prices.  The companies then engage in predatory pricing by undercutting the seafood prices offered by the fourth supermarket chain.  

A year later, the fourth supermarket chain closes its seafood department because it can no longer compete.  The three companies then modify their horizontal scheme: they push seafood prices far above the national average and take turns offering discounts in an effort to avoid accusations of violating antitrust laws.