The U.S. House of Representatives seat in North Carolina has remained vacant.
North Carolina election officials on Monday heard evidence on allegations.
The state officials had refused to certify the apparent victory by Republican Mark Harris over Democratic rival Dan McCready.
Allegedly the Harris campaign team had collected the incomplete absentee ballots.
The absentee ballots unlawfully collected by a Republican operative may have paved way for the victory of the Republican candidate in the Congressional election in November, it was stated by voters.
Trump has repeatedly and without evidence said that large numbers of illegal immigrants have cast ballots in U.S. elections.
He also said that Democrats benefited from the illegal immigrants casting ballots.
During the hearing witnesses said McCrae Dowless collected signed absentee ballots from voters which is against the law.
He was hired by the Mark Harris campaign.
The Republicans say even if that is true, the outcome of the election would stay the same and Harris is the clear winner.