A Democratic candidate for U.S. Senate in Georgia filed a lawsuit against his own party that alleges its leaders colluded with a deep-pocketed rival candidate.

John Coyne filed the lawsuit Thursday in Fulton County Superior Court that claims the Democratic Party of Georgia defrauded him by accepting his qualifying fee of $5,220 even though its leaders had an implicit agreement with Jim Barksdale as their preferred candidate.

The complaint said party leaders caused Coyne and another candidate, Cheryl Copeland, "great difficulty in their process of securing the support and fundraising needed to be elected." It seeks punitive damages from the state party, which did not immediately comment on the complaint.

Coyne, a businessman, flirted with a Senate bid in 2014 and ran unsuccessfully for a U.S. House seat in 2006. He's considered a long-shot candidate to win the May 24 primary.

Barksdale, a millionaire investment manager, was recruited and vetted by party leaders to run for the seat after a string of better known candidates passed on the chance to challenge Republican Sen. Johnny Isakson. He's already pumped more than $1 million into his campaign, funds he's already used to cover the airwaves with an introductory TV ad.

While the notion of a party having a preference for its nominee is nothing new (see: Hillary Clinton), rarely has it sparked a lawsuit. In his complaint, Coyne said Barksdale told him at an April forum that party leaders urged him to run shortly before he qualified.