CONNECTICUT — U.S. Senator Richard Blumenthal, D-CT, sent letters on Thursday to the commissioners of the NFL, NBA, NCAA, MLB, NHL and MLS raising concerns about sports gambling and prediction markets. In the letters, he asked the leagues to provide information by May 1 about their partnerships with sportsbooks and prediction markets and how they are safeguarding sporting integrity, preventing gambling addiction and protecting athletes from abuse.

"Since the federal ban on sports gambling -- a ban supported by the leagues -- was overturned eight years ago, gambling has permeated every aspect of the game," Blumenthal wrote. "The consequences of this rampant rise of sports gambling have been accelerating addiction, threats to players and even the corruption of the game."

He asked the leagues for a list of all partnerships with sportsbooks and prediction markets, the data shared between them and restrictions on the types of wagers offered. He also asked the leagues how they will ensure that any partnerships with prediction markets do not violate state laws, noting that states have sued to block prediction markets over their attempts to circumvent state gambling regulations. Last month, Blumenthal introduced legislation that would ban insider trading on prediction markets, restrict users under the age of 21 and make clear that prediction markets are not exempt from state oversight.

The MLS, NHL and MLB have all signed partnerships with prediction markets in the last six months, while the NFL and NCAA have publicly expressed concerns about the safeguards around prediction markets. The NCAA is the only one of the six organizations that does not have a commercial sportsbook partnership, though it signed a data sharing agreement with licensed sportsbooks last year.

MLB and MLS declined to comment on the letters. The NFL pointed to a letter it had sent to prediction market companies last month. An NHL spokesperson said the league is reviewing the letter. "We are extremely confident that we are taking all necessary steps to ensure the integrity and security of our games," the spokesperson said.

The NCAA said it has repeatedly called on state and federal regulators to rein in the types of bets offered by sportsbooks and to stop prediction market offerings on college sports. "The Association looks forward to working with the senator to explain the work the NCAA has been doing to protect student-athletes from the rise of sports betting," an NCAA spokesperson said.

Prediction market companies such as Kalshi have argued in courts across the country that they fall under the jurisdiction of the Commodity Futures Trading Commission, a federal agency, not state gambling regulators. A federal appeals court sided with Kalshi over New Jersey gaming regulators in a recent ruling. The CFTC also asked a judge to stop Arizona's criminal case against Kalshi and, in recent court filings, argued that it has exclusive jurisdiction over prediction markets. Last week, the CFTC sued three states, including Connecticut, over their attempts to regulate prediction markets.