A coalition of player associations representing the five largest professional sports leagues in the United States—the National Football League (NFL), Major League Baseball (MLB), the National Basketball Association (NBA), the National Hockey League (NHL), and Major League Soccer (MLS)—submitted a joint comment to the Commodity Futures Trading Commission (CFTC) on April 30, demanding a ban on certain types of sports event contracts offered by prediction market platforms such as Polymarket and Kalshi. The move directly pits the unions against the leagues themselves, several of which have established lucrative data and marketing partnerships with those same platforms.
Unions Target 'Negative-Outcome' and 'Mention' Contracts
Filed through lobbying firm Elevate Government Affairs on the final day of the CFTC's 45-day public comment period, the joint letter calls for a prohibition on contracts based on "negative outcomes" that could be manipulated by a single individual, including wagers on whether an athlete will be injured or penalized. The unions also requested a ban on "mention contracts" tied to specific words spoken during live broadcasts—such as "concussion"—labeling them "just another way to bet on a negative outcome."
The unions argued that prop bets on individual performances expose players and their families to harassment from disgruntled gamblers. They cited a New York Times survey published in The Athletic in November 2025, which found that 78% of professional baseball players reported that legalized sports betting had changed how fans treat them. "Individuals targeting our members do not distinguish between state-regulated bets and contracts offered on prediction markets," the unions wrote. "From their perspective, a bet is a bet regardless of where it is placed." The article also featured grim testimonials from NHL, NFL, and NBA players, though it made no mention of prediction markets.
Leagues' Commercial Ties Create Friction
Last year, the NHL became the first US professional league to enter the prediction market space, signing multiyear data partnerships with both Polymarket and Kalshi. MLB has Polymarket as its exclusive prediction market partner under a multiyear agreement and signed a memorandum of understanding with the CFTC regarding data sharing. MLS and the UFC have also inked marketing partnerships with prediction market operators.
The NBA, which has not entered into a similar partnership, submitted its own letter requesting that player prop markets be "banned in the near future until appropriate and reasonable restrictions are developed to mitigate risks threatening integrity." The PGA Tour, ATP Tour, and MLB also filed comments asking the agency to monitor susceptible markets. NBA's letter further called for raising the minimum trading age to 21, in line with the legal sports betting age in most US states.
CFTC Flooded with Over 1,500 Comments Amid High-Profile Scandals
The CFTC closed its 45-day rulemaking comment period on April 30 with more than 1,500 public comments received. Chairman Michael Selig defended the agency's stance in a letter to the editor published in the Wall Street Journal on May 1, writing that the CFTC has “exclusive jurisdiction over prediction markets” under the Commodity Exchange Act and warning that restrictive rulemaking would drive activity offshore.
Selig has repeatedly called exchanges self-regulatory organizations responsible for overseeing their own markets. This comes in the wake of scandals: in April 2024, Toronto Raptors forward Jontay Porter was banned for life for sharing confidential information with bettors who wagered on him to fall short of statistical 'under' limits. In October 2025, former Miami Heat guard Terry Rozier was arrested in a federal investigation into prop-bet manipulation, with prosecutors expected to file additional charges by mid-May.
Global Contrast: Brazil Bans Polymarket and Kalshi, Launches Bitcoin-Linked Contracts
Internationally, Brazil's stock exchange B3 announced it will launch six “event contracts” linked to the spot and mini futures of the Ibovespa index, the Brazilian real, and bitcoin. At the same time, Brazilian regulators have banned Polymarket and Kalshi from operating in the country. The simultaneous moves illustrate the divergent regulatory fates of prediction markets worldwide.
The unified action by US pro sports unions signals an escalating conflict between player welfare and league commercial interests, as regulators grapple with balancing innovation, integrity, and protection of athletes.