Investigators have subpoenaed several contributors to U.S. Rep. Jack Kingston’s failed Senate campaign to testify before a federal grand jury, The Atlanta Journal-Constitution has learned.

The contributors receiving subpoenas all have ties to Khalid Satary, a convicted felon and Palestinian national who helped organize a fundraiser for Kingston in late 2013 at Chateau Elan Winery and Resort in Gwinnett County.

Federal grand juries are secret and investigators are not revealing much about their probe, but a whistleblower involved in the fundraiser alleges the Gwinnett event involved illegal bundling of contributions in an attempt to curry favor with Kingston.

Kingston lost in a Republican primary runoff to eventual winner David Perdue. Subpoenas to several employees at Nue Medical Consulting and Confirmatrix Laboratories, two companies with ties to Satary that participated in the fundraiser, went out shortly after the Nov. 4 general election.

The AJC broke the story about Satary's links to Kingston's Senate campaign in June, and the resulting news coverage became an issue in the primary runoff. A pro-Perdue group ran television ads featuring Satary's photo and the tagline, "Georgia's Senate seat isn't for sale."

Kingston did not return requests for comment for this story, but in June he denied knowing about Satary’s criminal past in an interview with the AJC.

“These are not people I have a daily, weekly or regular discussion or correspondence with,” he said.

However, one of the donors, Confirmatrix vice president Richard Sasnett, was on Kingston's campaign finance committee. After his interview with the AJC, Kingston returned the contributions and removed Sasnett's name from the 200-member committee.

Federal officials have said Kingston, who is serving the final weeks of his 11th term in Congress, is not a target of their investigation. On Monday, FBI Special Agent Stephen Emmett said the agency had no comment on the status of the investigation.

Satary, also known as "DJ Rock," served more than three years in federal prison for running a counterfeit CD operation in the metro Atlanta area. At the time, the operation was valued at $50 million and was considered to be the largest such scheme in U.S. history.

Shortly after his release from prison in 2008, Satary was involved in founding Lawrenceville-based Confirmatrix, a urinalysis and drug-testing firm. He later founded Nue Medical in a nearby office complex, but subsequently transferred the company to his son, recent high school graduate Jordan Satary.

Satary is subject to a federal deportation order, but immigration officials have said they have been unable to find a country willing to accept him.

Satary’s attorney, Steve Sadow, would not comment on the subpoenas except that neither Satary or his son had received a subpoena. Stefan Passantino, an attorney and campaign finance expert representing Confirmatrix and its corporate officers, said his clients are cooperating with investigators.

The fundraiser drew more than $80,000 to Kingston’s Senate campaign and made Confirmatrix and Nue Medical his No. 1 and No. 4 donors, according to The Center for Responsive Politics, a non-partisan organization that tracks political donations.

The whistleblower, former Nue Medical employee Bill Miller, said he helped organize the fundraiser and a more intimate dinner with Kingston that followed. Miller said employees of the companies were given “bonus checks” before the event and were encouraged to pass most of the money along to Kingston. If true, such a “straw donor” scheme would violate federal law.

Miller, a veteran political consultant, said Satary hired him to clean up his reputation by re-branding the ex-con as an entrepreneur philanthropist. The fundraiser was part of that effort, Miller said.

In an interview this summer, Confirmatrix CEO Wes Warrington said the idea for the fundraiser came from Sasnett and that Nue Medical was brought in to provide logistical support. Warrington admitted employees received bonuses prior to the fundraiser and that Satary handed out some of the checks personally, but he denied they were encouraged to contribute to the Kingston campaign.

Donors at the event gave thousands of dollar each, despite the fact that the vast majority had never contributed to a campaign before, federal records show.

After the AJC began asking questions about Satary’s connection with the Kingston fundraiser, Confirmatrix announced it would sever its relationship with Nue Medical, the firm more closely tied to Satary and his son.