Democratic Rep. Adam Schiff called the Trump administration's decision to fire the deputy director of the FBI "harsh treatment" and said it had "an odious taint."

On Friday night, Attorney General Jeff Sessions fired Andrew McCabe, a 21-year veteran of the FBI who has been accused of approving unauthorized disclosures to the news media.

The firing came just one day before McCabe was set to retire.

Democratic Rep. Adam Schiff pushed back on Twitter against the firing of FBI deputy director Andrew McCabe, who was forced out of the bureau just one day before he was eligible to retire with full pension benefits.

"In the absence of the IG report, it’s impossible to evaluate the merits of this harsh treatment of a 21-year FBI professional," Schiff said in a tweet Friday night. "That it comes after the President urged the DOJ to deprive McCabe of his pension, and after his testimony, gives the action an odious taint."

The Department of Justice's inspector general office has been looking into McCabe's approval of unauthorized disclosures to the media in October 2016, related to the bureau's probe into Hillary Clinton's email use as secretary of state.

Attorney General Jeff Sessions, who announced McCabe's firing on Friday, said the inspector general's office and the Office of Personal Responsibility both concluded that McCabe made unlawful media disclosures and "lacked candor — including under oath — on multiple occasions."

The OPR issued a disciplinary proposal recommending McCabe's firing, Sessions added.

The full inspector general's office's report has not yet been made public.

Schiff, a congressman from California and the ranking Democrat on the House Intelligence Committee, has been one of Trump's leading critics.

Last month, he spearheaded a memo that attempted to undermine Republicans' claims that top officials at the FBI and the Department of Justice, including McCabe, improperly obtained a surveillance warrant to spy on a former member of the Trump presidential campaign.

McCabe has long been a punching bag for Republicans who believe he was part of a "deep state" within the US government trying to undermine President Donald Trump.

After repeated attacks by Trump and amid an internal FBI investigation into possible misconduct, McCabe stepped down from his post in January.

McCabe, a 21-year veteran of the bureau, was planning to retire on Saturday. His firing could put him at risk of losing his pension benefits.

"Here is the reality," McCabe said in a statement following his ouster. "I am being singled out and treated this way because of the role I played, the actions I took, and the events I witnessed in the aftermath of the firing of James Comey."

McCabe was one of three top FBI officials former FBI Director James Comey told about his conversations with Trump, many of which are now the subject of the special counsel Robert Mueller's investigation into whether Trump sought to obstruct justice when he fired Comey.