US Senate Minority Leader Harry Reid accused FBI Director James Comey of breaking federal law in disclosing possible new evidence in the Hillary Clinton email investigation.
Reid said in a letter sent to Comey that his disclosure to Congress, made 11 days before the election, might have violated the Hatch Act, which prohibits partisan politicking by government employees.
"Your actions in recent months have demonstrated a disturbing double standard for the treatment of sensitive information, with what appears to be a clear intent to aid one political party over another," Reid wrote.
"I am writing to inform you that my office has determined that these actions may violate the Hatch Act, which bars FBI officials from using their official authority to influence an election. Through your partisan actions, you may have broken the law."
While many Democrats and some Republicans have cast doubt on Comey's actions, citing Justice Department policies and precedent on handling investigations ahead of elections, Reid's letter is the most forceful denunciation levelled by a high-ranking elected official.