The federal government joined the bitter debate over college football's postseason system.
The Justice Department sent a letter Tuesday to the National Collegiate Athletic Association stating that "serious questions continue to arise" over whether the Bowl Championship Series—the sport's much-criticized method for choosing a champion—complies with antitrust laws.
The letter also asks why major-college football doesn't have a playoff, when so many other college sports do; what steps the NCAA has taken to create a playoff; and whether the NCAA has determined that aspects of the BCS system are unfair.
The letter, addressed to NCAA President Mark Emmert, is the latest and most dramatic event in a series of recent developments buffeting the BCS. In the past six weeks, the Fiesta Bowl fired its chief executive, John Junker, alleging financial improprieties. A group of law and economics experts wrote the Justice Department asking it to probe the BCS on antitrust grounds, and Utah Attorney General Mark Shurtleff said he intended to file an antitrust suit against the BCS.
At a congressional hearing Wednesday morning, Sen. Orrin Hatch (R., Utah), who has been pushing for an antitrust investigation of the BCS, asked Attorney General Eric Holder about the matter. Mr. Holder replied that the department had sent a letter to the NCAA and would be following up.
"We continue to receive information to determine whether to open an investigation into the legality of the current system under the antitrust laws," a Justice Department spokeswoman said.
Although the NCAA regulates college sports, its role in guiding major-college football has been diminished since a 1984 Supreme Court ruling, which found that it violated antitrust law in its television arrangements. Bob Williams, NCAA vice president of communications, said that Mr. Emmert has consistently said the NCAA was willing to create a playoff "if" the sport's membership makes that decision.
The BCS involves five games, one of which pits the No. 1- and No. 2-ranked teams against each other to determine college football's national champion. In the view of many critics, the rankings are subjective and discriminate against smaller schools.
The BCS started in the 1998 season, replacing two short-lived 1990s attempts to create a title game. For decades, college football struggled to produce a clear-cut title game because schools were contractually obligated to play in certain bowls, such as the Rose, Orange, Sugar and Cotton bowls. The BCS and its predecessors have tried to fix this by getting the No. 1- and No. 2-ranked teams to play each other. Auburn University beat the University of Oregon in this January's BCS title game, but Texas Christian University was left out of the championship matchup despite finishing its regular season undefeated.
BCS Executive Director Bill Hancock said he was confident the BCS complied with the law. "Goodness gracious, with all that's going on in the world right now and with national and state budgets being what they are, it seems like a waste of taxpayers' money to have the government looking into how college football games are played," he said.
To the BCS's many critics, however, the letter was a long-awaited sign that the government might take up the fight. Shortly after he was elected, President Barack Obama argued for a playoff on "60 Minutes" and said he would "throw my weight around a little bit."
"We aren't under any delusions that this is the No. 1 issue of the day," said Matthew Sanderson, co-founder of Playoff PAC, a political-action committee which is dedicated to replacing the BCS with a playoff. "But it's not trivial either."
—Thomas Catan contributed to this article.
Write to Darren Everson at darren.everson@wsj.com