In a complaint filed with the Federal Election Commission late last year, Kimberly Vertolli asserts that during Kirk's 2010 race for the Senate, his campaign may have improperly hidden payments to Jodie McCracken, by paying her through another company working for the campaign. McCracken's name does not appear in Kirk's federal disclosures, the Chicago Tribune reported Wednesday.
Kirk, who a campaign aide said is no longer in a romantic relationship with McCracken, denies any wrongdoing and views Vertolli's complaint as vindictive.
McCracken, who works in public relations, has said she received more than $143,000 in fees and expenses for her work on Kirk's campaign, the Tribune said.
Vertolli, a lawyer, was hired by the campaign after saying she would no longer support Kirk's candidacy, and was paid $40,000 after the election, the newspaper said.
Vertolli said she believes the money she received was to "get me to be quiet about my misgivings about McCracken."
Kirk campaign manager Eric Elk said in a written statement to the Tribune Vertolli has "filed a groundless complaint consisting of bitter personal attacks and is attempting to involve a federal agency in a divorce settled 36 months ago.
"We are saddened that she decided to file this ill-advised complaint and abuse the FEC process to air personal grievances," Elk said.
In a written response to the FEC, Kirk's lawyers said money paid McCracken did not have to be disclosed because she was a subcontractor to The Patterson Group, an ad firm.
Before winning the Senate seat previously held by President Barack Obama, Kirk, 52, served in the U.S. House of Representatives for a decade. He suffered a stroke in January and has made no public appearances since then. He declined the newspaper's request for an interview.