A judge in upstate New York on Monday was reviewing 2,500 challenged ballots that could determine the winner of the nation’s last undecided U.S. House race.

Entering the new year, former Rep. Claudia Tenney, a Republican, had a 29-vote lead over the incumbent Democrat, Rep. Anthony Brindisi.

The candidates have sparred in court over disputed affidavit and absentee ballots cast in their district in Central New York.

State Judge Scott DelConte was expected to spend the next few days reviewing ballots challenged by both campaigns. It’s unclear exactly when the process will wrap up. The judge’s review is likely to extend at least until next week.

Arguments about the ballots were made Monday with Brindisi's attorney saying votes cast at the wrong polling sites and ballots missing signatures should both be counted.

Tenney's attorney is arguing that ballots missing information, like whether they were a U.S. citizen, should also be counted.