WASHINGTON — A bipartisan group of influential senators is calling on the Biden administration to investigate Formula 1 over its decision to reject Andretti Global from racing on the grid in the coming years, suggesting the sport may be violating American antitrust law as it grows its U.S. fan base.

They made the request in a letter sent Tuesday and viewed by NBC News, which was led by Sen. Amy Klobuchar, D-Minn., the chair of the Judiciary subcommittee on antitrust, and joined by the panel’s ranking member, Sen. Mike Lee, R-Utah.

The letter is addressed to Jonathan Kanter, the assistant attorney general for the Justice Department’s Antitrust Division, and Lina Khan, the chair of the Federal Trade Commission — two entities that share enforcement of antitrust law.

It’s co-signed by Democratic Sens. Gary Peters and Debbie Stabenow of Michigan, whose state is home to General Motors, which has partnered with Andretti Global to build its engines. It’s also signed by Sen. Todd Young, R-Ind., who represents the state where Andretti is based, and Sen. Alex Padilla, D-Calif.

The six senators said they are “concerned” that F1 may be acting on behalf of other teams, “including foreign automakers,” to deny Andretti’s bid to enter the sport in 2025 or 2026 even though its governing body, the FIA, approved its application. Formula 1 management, the commercial side of the sport, rejected its bid in January, doubting the team would be competitive or increase the value of the championship.

“It is possible that such a refusal to deal—especially if orchestrated through a group boycott—could violate U.S. antitrust laws,” the senators wrote.

“Last year, F1 hosted three races in America, in Miami, Las Vegas, and Austin, while no other country hosted more than a single race,” they added. “Clearly there is a financial incentive to adding an American team to F1’s roster, and there is no reason they should be blocked unless [Formula 1 management] is trying to insulate its current partners from competition.”

The letter underscores rising interest by the U.S. government in the actions of F1 as it penetrates deeper into the American market with a growing fan base. A group of House members held a news conference with Mario Andretti on May 1 to pressure F1 to admit his team, and Judiciary Committee Chair Jim Jordan, R-Ohio, launched an independent inquiry the next week. A Justice Department or FTC probe would represent a significant escalation.

F1 and its American owner, Liberty Media, haven’t publicly responded to the allegations by members of Congress.

Andretti Global has expressed appreciation to lawmakers for getting involved in the clash within the international sport.

“We are grateful to the bipartisan members of Congress for their support in challenging this anti-competitive behavior,” a spokesperson for Andretti Global said this month. “We remain committed to bringing the first US works team and power unit to F1 and to giving American fans a home team to root for.”