Former U.S. Congressman Jesse Jackson Jr. has signed a plea deal with prosecutors who were investigating potential financial improprieties, according to a source close to Jackson's family.

Lawyers representing Jackson did not return CNN phone calls Friday, and the U.S. Attorney's office in Washington had no comment when asked about the Jackson case.

Last year, a law enforcement official told CNN that the FBI and federal prosecutors in Washington were investigating Jackson for possible financial improprieties. On Friday, the source told CNN that investigators are also looking at the possible involvement of Jackson's wife, Sandi Jackson, in those alleged improprieties. This official did not know if she might be charged in the investigation.

Sandi Jackson stepped down from the Chicago City Council on January 15, saying in a letter to Mayor Rahm Emanuel that she could not "deny my commitment to those most important personal responsibilities" of being a wife and mother.

She added her decision came "after much consideration and while dealing with very painful family health matters." She had held the seat since 2007.

Jesse Jackson Jr., who represented Illinois' 2nd Congressional District beginning in 1995, resigned in late November after winning election to a tenth term in the House. He was all but absent from the campaign trail this year, recording only an October robo-call message to constituents which said "a series of events came together in my life at the same time and they've been difficult to sort through."

He had not been seen in Washington or his district since last spring, and his office slowly revealed that he was receiving treatment for a mood disorder, depression and gastrointestinal issues at the Mayo Clinic in Minnesota.

The House Ethics Committee is separately looking into allegations that in 2008 Jackson, or one of his associates, offered to raise money for then-Illinois Gov. Rod Blagojevich in exchange for Jackson being appointed to the Senate seat vacated by Barack Obama.

"During my journey I have made my share of mistakes," former Rep. Jackson said in his November resignation letter to House Speaker John Boehner. "I am aware of the ongoing federal investigation into my activities and I am doing my best to address the situation responsibly, cooperate with my investigators, and accept responsibility for my mistakes, for they are my mistakes and mine alone."

Jackson is the son of the well-known civil rights leader. Reached Friday, the elder Jesse Jackson said "I have no comment regarding my son. I cannot confirm anything and if you are looking for that kind of information or confirmation it's not going to come from me."

Asked how his son was doing, Jackson said he was "taking his medication and handling his challenges."

A special election to fill Jesse Jackson Jr.'s House seat has been set for this spring.

 
CNN's Carol Cratty, Katherine Wojtecki and Kevin Liptak contributed to this report.