Florida gambling regulators have sent cease-and-desist letters to three daily fantasy-sports operators accused of offering potentially illegal mobile betting games and threatened legal action if the sites don’t immediately stop.

Commission Executive Director Lou Trombetta sent letters warning the three companies that they “may be offering or accepting illegal bets or wagers” from Floridians and “may be promoting and conducting an illegal lottery.”

The alleged conduct is “strictly prohibited in Florida and constitutes criminal activity,” Trombetta wrote.

The letters targeted Underdog Sports, LLC, which is based in Brooklyn, N.Y; SidePrize LLC, also known as Performance Predictions LLC, doing business as PrizePicks, which is based in Atlanta; and Betr Holdings, Inc., which is based in Miami.

In fantasy sports, players can draft rosters of actual athletes, with the winners of fantasy games determined by the statistics of the athletes. Many games, like office pools, last all season.

The three companies offer what are known as “parlay-prop-style” games that could be more similar to sports-betting games that are off-limits in Florida.

“Under Florida law, betting or wagering on the result of contests of skill, such as sports betting, including fantasy sports betting, is strictly prohibited and constitutes a felony offense unless such activity is otherwise exempted by statute,” Trombetta’s letter said. “Accordingly, in Florida, sports betting may be lawfully conducted only pursuant to a gaming compact. … Further, receiving such illegal bets and wagers and aiding or abetting such criminal activities constitute separate felony offenses. … Lotteries are also strictly prohibited in Florida.”

A gaming compact is an agreement reached with the state.

The commission did not send letters to DraftKings and FanDuel, which have dominated the fantasy-sports market in the decade since the online games launched.

It was unclear Friday if the commission would crack down on other operators in the future, but emails show the gambling overseers could be casting a broad net.

“As you might imagine, my exec team asking what the letter means and seeking actionable advice, pretty urgently. Would like to discuss the substance at some point, but if you can help with one question, it would be great. Namely, Underdog operates multiple paid fantasy formats (season-long drafts, daily drafts, pick’em) and I just want to confirm my reading of the letter, which is that the legal conclusion applies to all paid fantasy contests — e.g., all of our contests — and not just particular types,” Nicholas Green, Underdog’s general counsel, wrote Friday to Ross Marshman, the commission’s general counsel.

“Your reading of the letter is correct,” Marshman replied.

John Lockwood, an attorney hired by multiple operators, warned that other companies could be swept up in the crackdown.

“The commission staff confirmed to me that the language in the letter broadly applies to all paid fantasy sports contests, and they are not aware of any paid fantasy sports company operating legally in Florida. We disagree on the merits and will be working with the commission and potentially the Legislature so we can ensure Florida sports fans can continue to play,” Lockwood said.

State lawmakers in the past have grappled with creating regulatory oversight for the fantasy-sports industry, to no avail. Proponents of fantasy sports have insisted that the contests are games of skill, not chance, and thus are legal under state gambling laws.

Trombetta issued the letters as a legal battle continues over a 2021 compact reached by the state and the Seminole Tribe. That deal gave the tribe control over sports betting in Florida.

A “hub and spoke” plan in the agreement would allow gamblers anywhere in the state to place bets online, with the wagers run through servers located on tribal lands. The deal requires sports betting to be “exclusively conducted” by the Seminoles but allows other operators to run fantasy sports contests.

Owners of West Flagler Associates and Fort Myers Corp., doing business as Bonita Springs Poker Room in Southwest Florida, filed a lawsuit challenging the compact, saying it violated federal law and would cause a “significant and potentially devastating impact” on their operations.

A federal judge in Washington, D.C., in November 2021 ruled that the deal violated a key Indian gambling law. But a three-judge panel of the U.S. Circuit Court of Appeals for the District of Columbia in June reversed that decision. The appellate court last week denied a request for what is known as an “en banc” rehearing before the full court.

The pari-mutuel owners filed a motion saying they would ask the U.S. Supreme Court to weigh in, arguing the panel’s decision conflicts with other appellate rulings and “enables an extreme shift in public policy on legalized gaming that, once started, may be difficult to stop.”