"While the facts of the case involving General David Petraeus remain unknown and are not suitable for comment, it is clear that this investigation has been grievously mishandled," McCain and Graham said in a joint statement.
Justice Department prosecutors are recommending charges be filed against Petraeus for disclosure of classified information, a federal law enforcement official told CNN on Friday. The New York Times was first to report that the charges had been recommended.
The official said the FBI has provided sufficient evidence to the Department of Justice to bring felony charges against Petraeus for providing classified information to former mistress Paula Broadwell while he was the director of the CIA.
He allegedly provided documents to Broadwell, who was working on a book with the former director.
The statement from McCain, a Republican from Arizona, and Graham, a Republican from South Carolina, said: "It is outrageous that the highly confidential and law enforcement-sensitive recommendation of prosecutors to bring charges against General Petraeus was leaked to the New York Times. It is a shameful continuation of a pattern in which leaks by unnamed sources have marred this investigation in contravention to fundamental fairness.
"No American deserves such callous treatment, let alone one of America's finest military leaders whose selfless service and sacrifice have inspired young Americans in uniform and likely saved many of their lives."
Attorney General Eric Holder will have to ultimately decide whether to seek an indictment against the prominent military officer. The CIA and Justice Department had no comment.
The official says the Department of Justice has had the information "for a little while."
An attorney for Petraeus did not respond to a request for a comment.
In 2012, Petraeus told CNN's Kyra Phillips that he never passed classified information to Broadwell.
According to a source familiar with the investigation, Petraeus used an alias based on the Keanu Reeves character in the movie "Point Break" -- Special Agent Johnny Utah -- to correspond with Broadwell, who went by the name Tyler, Johnny Utah's girlfriend in the film.