Comey, fired by President Donald Trump last month while leading a Federal Bureau of Investigation probe into Russian meddling in last year's US presidential election, was slated to appear before the Senate Intelligence Committee at 10 a.m. EDT.
During nearly three hours of his explosive testimony to a Senate panel, Comey said he saw Trumps request to stop investigating the alleged ties of his former national security adviser Michael Flynn as an "order". That includes former national security adviser, Michael Flynn.
Kasowitz says that the president is "entitled to expect loyalty" from those serving the administration.
Mr Comey revealed he had leaked one of his memos about the "disturbing" conversations with Mr Trump - asked whether he thought the President had taped their encounters he quipped "Lordy, I hope there are tapes".
"It's my judgment that I was sacked because of the Russian Federation investigation", Comey told the Senate intelligence committee in explosive testimony that threatened to undermine Trump's presidency.
The new complaint will focus on Comey's testimony that he gave a friend the content of memos about his conversations with Trump and asked the friend to then give that information to a reporter.
For instance, senators received this particular response when Comey was questioned about the dossier compiled by a British spy and whether he believed President Donald Trump colluded with Russian Federation.
Trump's private attorney, Marc Kasowitz, seized on Comey's affirmation that he told Trump he was not personally under investigation.
"Comey's excuse for this unauthorized disclosure of privileged information. appears to be entirely retaliatory", Kasowitz said in the statement.
Trump had stayed unusually quiet on Thursday, refraining from weighing in on the testimony gripping the country both on Twitter and at several public appearances. Telemundo, in the moments before Comey started, also showed a simulated reconstruction of Trump and Comey meeting in the White House, with conversations in Spanish printed in cartoon-like bubbles over their heads.
On CNN, the message read "Comey: I took Trump's request about Flynn as a directive".
A day after Trump sacked Comey, Trump told two senior Russian envoys in the Oval Office that Comey was "crazy, a real nut job", according to leaked accounts of the conversation.
Comey said he chose to use a go-between because he was anxious about the increased media scrutiny the memo was likely to bring.
"In sum, it is now established that there the president was not being investigated for colluding. or attempting to obstruct that investigation", he said. He's still the man who helped get us into this fucked-up mess by inserting himself into the election with his "Hey, y'all, I have something to say about Hillary Clinton's emails" bullshit. He also excoriated Comey for leaking to the press.
In his testimony former Federal Bureau of Investigation director James Comey echoed a view that I alone have been expressing for several weeks, and that has been attacked by almost every Democratic pundit.