BOSTON (AP) — The Federal Trade Commission is seeking to block the merger of FanDuel and DraftKings, the two largest daily fantasy sports sites.

The FTC said Monday that it, along with the attorneys general of California and the District of Columbia, will file a complaint to temporarily stop the deal pending an administrative trial.

The commission said the company created by combining the two sites would control more than 90 percent of the U.S. market for paid daily fantasy sports contests.

The CEOs of the onetime rival companies said in a statement that they’re disappointed by the decision and are weighing their options.

Daily fantasy sports contests are online games in which players build rosters of real-life athletes and compete for cash and other prizes based on how those athletes do in actual games.

FanDuel advertising covers the post for an NCAA college basketball matchup in the FanDuel Legends Classic consolation game, Tuesday, Nov. 24, 2015, at the Barclays Center in New York. (AP Photo/Kathy Willens)
AP

FanDuel advertising covers the post for an NCAA college basketball matchup in the FanDuel Legends Classic consolation game, Tuesday, Nov. 24, 2015, at the Barclays Center in New York. (AP Photo/Kathy Willens)

FILE- In this Sept. 9, 2015, file photo, Len Don Diego, marketing manager for content at DraftKings, a daily fantasy sports company, works at his station at the company’s offices in Boston. New York’s attorney general has sent letters to daily fantasy sports websites DraftKings and FanDuel demanding they turn over details of any investigations into their employees on Tuesday, Oct. 6, 2015. (AP Photo/Stephan Savoia, File)
AP

FILE- In this Sept. 9, 2015, file photo, Len Don Diego, marketing manager for content at DraftKings, a daily fantasy sports company, works at his station at the company’s offices in Boston. New York’s attorney general has sent letters to daily fantasy sports websites DraftKings and FanDuel demanding they turn over details of any investigations into their employees on Tuesday, Oct. 6, 2015. (AP Photo/Stephan Savoia, File)
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