The U.S. Senate voted unanimously on Thursday to bar its members, staff, and other chamber officials from participating in prediction markets, effective immediately.

The resolution, introduced last Friday by Sen. Bernie Moreno (R-Ohio), amends Senate rules to prohibit members from entering into any agreement, contract, or transaction dependent on the outcome of a specific event. Moreno argued that senators have no business in speculative activities like prediction markets while drawing taxpayer salaries. "United States Senators have no business engaging in speculative activities like prediction markets while collecting a taxpayer-funded paycheck, period," Moreno said.

The move addresses growing concerns over insider trading risks, as lawmakers possess nonpublic information that could give them an edge on platforms such as Kalshi and Polymarket. Recent incidents heightened scrutiny. At least 16 accounts profited more than $100,000 each by correctly predicting a U.S. and Israeli strike on Iran's supreme leader in February, hours before the attack. On April 23, Army Master Sgt. Gannon Ken Van Dyke faced arrest for allegedly using classified information to bet on Polymarket about the capture of Venezuelan leader Nicolás Maduro, netting nearly $410,000. Kalshi also fined and suspended three congressional candidates last week for betting on their own elections.

Senate Minority Leader Chuck Schumer (D-N.Y.) praised the action as "a good thing that the Senate is moving swiftly" and called on the House and the administration to follow suit. He vowed to ensure executive branch officials cannot profit from such markets after mid-May.

Polymarket expressed support on X, noting its rules already prohibit the conduct and welcoming codification into law. Sen. Todd Young (R-Ind.) described the ban as a "good first step," referencing his bipartisan bill with Sen. Elissa Slotkin (D-Mich.) to prohibit federal officials from using insider information on prediction markets.

The resolution reflects broader congressional unease with prediction markets' rise amid geopolitical tensions and political events. Several bills target restrictions, including bans on sports bets, election wagers, and government action contracts, though the Senate rule applies only internally. No similar House measure has passed yet.