(CNN) House Oversight Chairman Jason Chaffetz asked the inspector general for the Justice Department Wednesday to expand his probe of the FBI's handling of the Hillary Clinton email investigation to also review FBI Director James Comey's firing by President Donald Trump.

Justice Department Inspector General Michael Horowitz first opened a probe into the Clinton email investigation in January. At the time, Horowitz said it may be expanded "if circumstances warrant."

"You stated previously that your work includes an examination of whether Comey's public communications and notifications to Congress about the Clinton investigation comported with Justice Department and FBI policies and procedures. You separately stated 'if circumstances warrant, the OIG will consider including other issues that may arise during the course of the review,'" Chaffetz wrote in his letter to Horowitz. "The recommendation to remove Comey indeed warrants such consideration."