The NFL is taking its fight over prediction markets to the Supreme Court.

In a friend-of-the-court brief filed Thursday, the league backed New Jersey in its legal battle with Kalshi. It asked the justices to decide whether states or the federal government should regulate sports contracts on these platforms. The NFL argues the contracts are sports gambling, not financial swaps, CBS News reported. Two federal appeals courts, the 6th and 9th Circuits, have ruled the same way.

The league was represented by former U.S. Attorney General Bill Barr and his law firm, Law.com reported.

Prediction markets let users buy contracts on the outcome of events, including games. They are overseen by the Commodity Futures Trading Commission, a federal agency. But at least 10 states have sued the platforms, saying their sports contracts are gambling under state law. Federal appeals courts have split on the question.

The money is large. On the first Sunday of the season, football drew $1.8 billion in prediction-market trading, more than half the total, the NFL told CNBC.

The league says it is not against prediction markets. It worries about bets that are easy to rig, like a kicker missing a field goal on purpose, and about bets tied to injuries or officiating. It also wants a minimum age of 21, as most states require for sports betting. Kalshi lets users trade at 18.

The NFL asked for a ruling before the season ends in January. Any delay, it wrote, will "result in increasing consumer harm and risk to game integrity." A group of states from both parties filed a similar request a day earlier.

Kalshi pushed back. A spokesperson said the CFTC's ongoing rulemaking addresses many of the league's concerns. Kalshi also said it has tried to work with the NFL on market integrity but got no response.

Other leagues have taken a different path. The NHL has deals with Kalshi and Polymarket, and Major League Baseball has one with Polymarket.

What we know: The NFL, New Jersey and a group of states want the Supreme Court to settle who regulates sports prediction markets.
What we don't: Whether the justices will take the case, and when.