Republican Randy Altschuler's lead over Rep. Tim Bishop (D-N.Y.) is now below 300 votes in what has been a contentious manual count of ballots in the state's 1st congressional district.

Bishop's campaign said Thursday that it had picked up more than 100 votes after all precincts in Republican-heavy Smithtown and Southampton reported their totals.

"The fact that we have picked up this many votes in just two towns, including a Republican stronghold, is an extremely encouraging sign," Bishop spokesman Jon Schneider said in a statement. "The momentum is clearly on Tim Bishop’s side and we are confident we will win this election."

The counting process has been fraught with tension, which erupted earlier this week upon news that Altschuler's campaign was challenging the absentee ballots cast by Bishop's elderly parents.

On Wednesday, Bishop called the move "despicable" in an interview with The Hill.

"My father is about to be 87 and quite infirm," Bishop said. "I don't want to be melodramatic, but arguably this is the last election for which he's going to be alive. So for my opponent or the people working for my opponent to deny him the right to vote in general and specifically the right to vote for me, I just think it's despicable."

Bishop also issued a fundraising plea Wednesday using his father's story, noting that he's an eleventh-generation resident of Southampton.

A spokesman for Altschuler said the campaign flagged all absentee ballots that were mailed out of state because many people have second homes in the Hamptons, which is in New York's 1st district. Bishop's father mailed his ballot from Florida.

—Sean J. Miller contributed to this post.