In an e-mail sent Friday, an official in the department's Public Integrity Section said prosecutors can publicly announce suspected election fraud that involves federal employees like postal workers before the polls close, according to the reports.
The Justice Department did not immediately respond to a request for comment.
The email, first reported by ProPublica, called the policy an "exception" to a decades-old Justice Department policy that discourages prosecutors from taking overt investigative steps in election fraud investigations until ballots have been counted.
In a 2017 memo, the Justice Department said publicly announcing investigations right before the election "runs the obvious risk of chilling legitimate voting and campaign activities" and "runs the significant risk of interjecting the investigation itself as an issue" in the campaign.
The change in policy is "deeply concerning," said Miriam Aroni Krinsky, executive director of Fair and Just Prosecution, a criminal justice reform group. "There is simply no reason to depart from that sensible starting point that has guided federal prosecutors for years," she said.
President Donald Trump has repeatedly claimed without evidence that a rise in mail-in voting will lead to a rise in fraud.
The U.S. Attorney's Office in New Jersey on Wednesday announced the arrest of a postal worker accused of discarding about 2,000 pieces of mail, including about 100 blank general election ballots. The Justice Department said the evidence does not indicate that the postal worker's actions were politically motivated.
On Sept. 24, a federal prosecutor in Pennsylvania announced an inquiry into a small number of military ballots that allegedly had been “discarded,” some of which were cast for Trump. A local official discovered the ballots and reported the matter to law enforcement authorities.
Some former Justice Department officials criticized the public statement in that case, saying there was no legitimate reason to disclose that the ballots were marked for Trump.