WASHINGTON -- The Justice Department wants to know why the NCAA doesn't have a college football playoff system and says there are "serious questions" about whether the current format to determine a national champion complies with antitrust laws.

Critics who have urged the department to investigate the Bowl Championship Series contend it unfairly gives some schools preferential access to the title championship game and top-tier end-of-season bowls.

In a letter this week, the department's antitrust chief, Christine Varney, asked NCAA president Mark Emmert why a playoff system isn't used in football, unlike in other sports; what steps the NCAA has taken to create one; and whether Emmert thinks there are aspects of the BCS system that don't serve the interest of fans, schools and players.