Mellow is now scheduled to appear before a federal judge in Scranton on May 9. He was charged in March with misusing Senate staff and resources for political fundraising and campaigning.
The 69-year-old Mellow had been scheduled to plead guilty last week but The Times-Tribune of Scranton ( http://bit.ly/JaolJp) reports the judge assigned to the case was presiding over another trial.
Under the terms of a plea agreement Mellow could face up to five years in prison.
Mellow served 40 years in the Senate and was one of the chamber's most powerful members when he announced his retirement two years ago.
Information from: The Times-Tribune, http://thetimes-tribune.com/