Illinois Gov. J.B. Pritzker, along with his wife and brother-in-law, reportedly is under federal criminal investigation for a questionable property tax appeal that has hung over him since last year’s gubernatorial race.

Pritzker – a Democrat who took office earlier this year – has been the subject of an ongoing criminal investigation since last October, although no criminal charges have been brought against him, a law enforcement source told Chicago radio station WBEZ.

"I'm very confident that any review of this matter will show that all the rules were followed," Pritzker said Wednesday during a press conference. "I have not been contacted by any law enforcement, neither has MK (Pritzker's wife)."

Pritzker went on to call the matter "a political issue" raised by his opponents during last year's gubernatorial campaign and said he was focused on his work as governor.

The investigation centers around a property tax break the billionaire Pritzker and his wife sought for a 126-year-old mansion the two purchased. According to a Cook County inspector general’s report, which was first discovered by the Chicago Sun-Times newspaper, Illinois First Lady MK Pritzker ordered workers at the mansion to remove all the toilets in the residence so it could be declared “uninhabitable” – giving the couple a large tax break.

The Department of Justice did not immediately respond to Fox News' request for comment.

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The report also said that the governor’s brother-in-law, Thomas J. Muenster, and the first lady’s personal assistant, Christine Lovely, made false representations on tax appeal documents. The scheme apparently cost taxpayers more than $331,000, according to the IG report.

Marc Elias, a lawyer representing the Prtizkers, added to WBEZ that neither the governor nor his wife has been contacted by law enforcement officials about the matter, and denied any wrongdoing on the part of his clients.

“Neither the Governor nor the First Lady have been contacted by law enforcement regarding the property tax appeal,” Elias said. “We are confident that any further review of the matter will show that the appropriate rules were followed.”

The reports of the investigation into Pritzker, who just celebrated his 100th day in office, were quickly flagged by political rivals, who called him out for seeking tax breaks while he has proposed raising taxes.

“An Illinois governor under federal criminal investigation 101 days into office must be a new record - even for Illinois,” Illinois Republican Party Chairman Tim Schneider said in a statement. “We already knew Pritzker was a serial tax dodger. He stashes millions offshore in zero-tax Bahamas bank accounts and took the toilets out of his Chicago mansion to dodge over $330,000 in property taxes.”

Schneider added: “The Cook County Independent Inspector General called it 'a scheme to defraud' taxpayers. Yet Pritzker continues to push tax hikes on Illinois families and businesses - absurd hypocrisy from Pritzker.”

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The Chicago Tribune reported last year that Pritzker used offshore banking in the Bahamas to avoid paying taxes on his family’s fortune. Pritzker acknowledged the offshore accounts but argued that they were originally set up long ago by his grandfather.

“Any trusts for my benefit that are offshore, I have received no distributions from, and those trusts are only providing charitable contributions,” Pritzker, an heir to the Hyatt Hotels chain, told the newspaper. “That’s all that they do.”

The newspaper, however, found several offshore shell companies created between 2008 and 2011 – long after his grandfather’s death – that were either totally owned by Pritzker and his brother, or by close associates of the now-governor.