Bipartisan pair of Senators press Kalshi, Polymarket over election markets

A bipartisan pair of senators are pressing Kalshi and Polymarket over prediction markets tied to the Nov. 3 midterm elections.

“We write to express concerns about election-related prediction markets and to request specific information about your companies’ efforts to prevent insider trading, market manipulation, and wagers based on material nonpublic information,” Sens. Elizabeth Warren (D-Mass.) and John Curtis (R-Utah) wrote in a letter addressed to Kalshi CEO Tarek Mansour and Polymarket CEO Shayne Coplan.

The senators were particularly concerned with “ election-related event contracts ” which are a type of asset class that gives users the ability to make trades about a specific yes or no question. It referenced several instances where candidates bet on their own races in 2025 and April 2026 on Kalshi, warning “these examples raise critical questions about how many election-related transactions have escaped detection.”

The letter also cited alleged market manipulation tactics on Polymarket during the 2024 presidential election affecting “roughly one-third of the presidential market’s trading volume,” according to one Fortune report .

A source from Kalshi said the company already “proactively” blocks candidates and staffers from trading on election markets using Federal Election Commission (FEC) payroll data as well as forming an independent market integrity committee to combat possible insider trading.

The senators asked both companies to provide the steps it had previously taken to prevent possible insider trading from campaigns and “other individuals with access to material nonpublic information” beyond using FEC filings. Their letter also asked what instances of election-related insider trading had been referred to the Commodities Futures and Trading Commission (CFTC) and what safeguards were currently in place.

“We remain skeptical that your companies can sufficiently police these even contracts with effective scrutiny and meaningful accountability,” the senators concluded.

The source added Kalshi looks forward to demonstrating how it keeps its platform free of insider trading.

Warren and Curtis’s letter follows up on Utah Attorney General Derek Brown (R) criminally charging Mansour along with other prediction market heads, alleging they illegally profited from promoting and offering online gambling within the state.

They face 13 felony counts and one misdemeanor count, according to a recent court filing.

In response to the letter, Kalshi’s head of enforcement Robert DeNault told The Hill, “Kalshi prohibits insider trading and market manipulation and proactively blocks candidates and campaign staff from trading to protect market integrity.”

“While fake polls have recently been promoted by major media outlets, our markets don’t lie—and have been largely non-reactive to fake information or attempts to distort the odds of candidates with big trades,” DeNault continued.

Polymarket did not immediately respond to The Hill’s request for comment.