The National Football League has picked a side in the fight over prediction markets. In a 24-page brief filed Thursday, the NFL urged the Supreme Court to back state gambling regulators, who argue that these sports contracts should follow the same rules as traditional bets.The NFL argued that states have long regulated gambling and that sports prediction contracts are bets on game outcomes instead of tools that help businesses protect themselves from financial losses. It pointed to the nearly $2 billion traded on NFL games through prediction market platforms alone on the opening Sunday of the 2026 season—more than half of the day’s total prediction market volume—and urged the Supreme Court to act “before another NFL season goes by.” The top court has not agreed to hear the case, but it is widely expected to take up the matter next year.The Commodity Futures Trading Commission, which regulates financial products including swaps—contracts with payments tied to price changes or event outcomes—has taken a largely hands-off approach to prediction markets under the current administration, allowing federally registered exchanges like Kalshi to offer sports contracts without following traditional state gambling rules.Thursday’s brief confirmed the NFL’s suspected resistance to the rapid growth of event contract platforms. Citing independent research, it said sports contracts account for 80% of Kalshi’s trading volume and that the platform recorded more than $173 billion in trades through late August 2026, compared with $25 billion across all registered exchanges in 2025. By contrast, other sports associations including Major League Baseball, Major League Soccer, and the National Hockey League have embraced prediction markets through partnerships with Kalshi and Polymarket.“Polymarket shares the NFL’s commitment to preserving the integrity of the game, which is why we … are actively collaborating with the CFTC, SEC, and other professional leagues toward a harmonized federal framework,” Polymarket said in a statement.Kalshi did not immediately respond to Fortune’s request for comment. The legal fight over prediction markets came to a head in late August, when the Ninth Circuit allowed Nevada regulators to enforce state gambling laws against Kalshi’s sports contracts, creating a split between federal appeals courts. Nevada’s Gaming Control Board had ordered Kalshi to stop offering the contracts without a state gaming license. Kalshi argued that the CFTC’s authority over its platform meant state gambling laws did not apply.The ruling created a split with the Third Circuit, which had sided with Kalshi in its dispute with New Jersey regulators in April. That court classified Kalshi’s sports prediction contracts as swaps rather than bets governed by state gambling laws.The split widened last month, when the Ninth Circuit reaffirmed its position in a separate case involving the Blue Lake Rancheria tribe, and the Sixth Circuit allowed Ohio and Tennessee to enforce their gambling laws against Kalshi’s sports contracts while the lawsuits continued.In its amicus brief, the NFL sided with the Sixth and Ninth Circuits, agreeing with their position to treat sports prediction contracts as gambling rather than financial products. The league urged the Supreme Court to resolve the split, arguing that conflicting rulings leave oversight unclear and raise concerns about cheating, insider trading, and consumer protection.This story was originally featured on Fortune.com