Citing four people with knowledge of the case, the newspaper reported that investigators were reviewing Perdue's trading for "possible evidence of insider trading."

Scott Grimes, co-founder and CEO of Cardlytics at the time, sent an email to Perdue two days before the stock sale that mentioned "upcoming changes." According to the Times, investigators concluded it "contained no meaningful nonpublic information and declined to pursue charges, closing the case this summer."

In a statement to CNN, Casey Black, a spokesperson for Perdue, said, "Separate reviews by the Department of Justice, the Securities & Exchange Commission, and the bipartisan Senate Ethics Committee each quickly and independently cleared Senator Perdue of any wrongdoing.

"Senator Perdue has always followed the law," Black said in the statement.

CNN reached out to the Justice Department for comment Thursday.

Democrat Jon Ossoff, who will face Perdue in a runoff election in January, has criticized his opponent over the alleged stock sales, contending that the Republican declined to debate him in October over the incident.

During an interview with CNN's Kate Bolduan Wednesday night, Ossoff called Perdue "a crook who abused his office to enrich himself."

Congress passed the Stock Act in 2012, which made it illegal for lawmakers to use inside information for financial benefit.