NEW YORK, Sept 16 (Reuters) - Major League Baseball's players union sued DraftKings ( DKNG ) and FanDuel on Monday, accusing the sports betting companies and two others of using the names and likenesses of hundreds of players on their platforms without permission.

Players are seeking compensatory and punitive damages from DraftKings ( DKNG ) and Britain's bet365 Group in Philadelphia federal court, and from FanDuel and Brooklyn-based Underdog Fantasy in a New York state court in Manhattan.

Calling online sports betting "big business," MLB players accused the defendants of "flagrant" violations of state laws protecting the right of publicity, saying nearly every active player's image appears on their websites and mobile apps.

"For professional athletes, the ability to control the commercial use of their names, images, and likenesses is a crucial return on their substantial career investment," the players said.

Keeping such control also helps players avoid being perceived as supportive of companies and products they dislike, the players added.

DraftKings ( DKNG ), FanDuel and Underdog did not immediately respond to requests for comment. Bet365 could not immediately be reached after business hours. The players' lawyers did not immediately respond to requests for additional comment.

Monday's lawsuits were filed three weeks after the National Football League players union, represented by the same law firm as the MLB players, sued DraftKings ( DKNG ) for refusing to pay for using NFL player likenesses on so-called non-fungible tokens.

In Monday's complaints, the MLB players said the defendants don't use NFL player likenesses on their platforms.

They said the only reason to treat baseball players differently was to increase "consumer appeal" and draw more bets, given that the "core information" that bettors need is statistical data, not what players look like.

Users, for example, could bet that the Philadelphia Phillies' Bryce Harper or New York Mets' Pete Alonso will hit more than two home runs in a given game, without seeing each player's "valuable image," the complaints said.

The cases are MLB Players Inc v DraftKings Inc ( DKNG ) et al, U.S. District Court, Eastern District of Pennsylvania, No. 24-04884; and MLB Players Inc v. Underdog Sports Inc et al, New York State Supreme Court, New York County.