INDIANAPOLIS (AP) — The Indiana Democratic Party is challenging the U.S. Senate candidacy of Republican U.S. Rep. Todd Young.

Democrats say Young is two shy of the required number of petition signatures in northwestern Indiana’s 1st Congressional District. State law requires Senate candidates to submit signatures of 500 registered voters from each of Indiana’s nine congressional districts to qualify for the May primary ballot.

Democrats filed a formal complaint with the state Election Division Wednesday morning.

Young’s campaign dismisses the move as a “political stunt,” saying it turned in nearly 650 signatures for the 1st District.

Young represents southern Indiana’s 9th Congressional district. He is running for the seat of retiring Republican Sen. Dan Coats.

U.S. Rep. Marlin Stutzman is the other GOP candidate running for the seat.