WASHINGTON (Reuters) - Two U.S senators have asked the Federal Trade Commission and Justice Department to investigate online betting platforms DraftKings ( DKNG ) and FanDuel over concerns they are coordinating against competitors.

In a letter dated Dec. 5, Republican Senator Mike Lee and Democratic Senator Peter Welch asked for an investigation following reports that the two companies were allegedly acting together to pressure businesses not to engage with competitors.

"After their merger to monopoly was blocked, it seems that FanDuel and DraftKings ( DKNG ) have arguably acted as one company, violating our antitrust laws," they wrote, citing the companies' failed 2016 plan to combine. Lee posted the letter on social media platform X.

Representatives for the two companies, the FTC and the Justice Department could not be immediately reached for comment.

Shares of DraftKings ( DKNG ) were last down about 2.6% in late morning trade on the Nasdaq.