The House Oversight Committee has launched an investigation into prediction markets Kalshi and Polymarket over concerns about insider trading.

Committee Chair James Comer told CNBC’s “Squawk Box” on Friday that he sent letters to Polymarket CEO Shayne Coplan and Kalshi CEO Tarek Mansour requesting internal documents on identity verification, geographic restrictions, and anomalous trading detection, with a deadline of June 5.

The probe follows rising scrutiny from lawmakers after several high-profile incidents, including a US soldier allegedly profiting from classified knowledge and congressional candidates betting on their own races.

Comer stated that access to internal company records is necessary to determine whether users are engaging in insider trading and whether the platforms are adequately enforcing legal safeguards.

Comer said that the probe aims to build a case for legislation that would ban government employees and members of Congress from participating in these markets.

Prediction markets have seen rapid growth in recent years, allowing users to bet on outcomes involving elections, sports events, policy decisions, and entertainment awards. Their growing influence has also raised concerns among lawmakers and regulators about the possibility that individuals with privileged government information could use the platforms for personal profit.

Kalshi has faced separate criticism after several political candidates were found betting on their own campaigns through the platform. In April, the company suspended three congressional candidates linked to those wagers.

Lawmakers from both parties are pushing for tighter regulation of prediction markets. Several bills introduced in Congress seek to address insider trading and other issues connected to online betting platforms.

Comer’s investigation also follows a request from Democratic lawmakers led by Rep. Chris Pappas asking the Oversight Committee to subpoena prediction market companies.