Democrats, Republicans Pressure FBI Director Comey After New Email Revelation

The FBI said new emails may be part of investigating Clinton's private server.

On Friday, Comey sent a letter to Congress notifying top Republicans and Democrats that the FBI had uncovered emails that "appear to be pertinent to the investigation" into Clinton through a separate probe.

Comey said it’s not clear if those emails –- uncovered through an investigation into former New York Rep. Anthony Weiner’s alleged lewd messages to an underage girl in North Carolina –- would contain information relevant to the Clinton probe.

"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," he wrote.

The FBI has blamed Russia for a series of cyberattacks against U.S. political institutions.

Reid's office has not yet responded to ABC News' request for comment regarding purported evidence of ties between Trump’s campaign and the Russian government.

Another Democrat, Rep. Steve Cohen, D-Tennessee, a member of the House Judiciary Committee, has called on Comey to resign over the episode. He said in an interview on CNN Monday that he believes Comey’s actions could cost Hillary Clinton the election.

"I didn't understand the purpose of the letter," Gonzales, a Republican who is not supporting Donald Trump’s campaign, told CNN in an interview.

The FBI declined ABC News' request for comment.

ABC News' Ali Rogin contributed to this report.