The FBI is investigating a Long Island Democratic Party boss after claims from insiders that he tried to buy votes to guarantee his reelection, sources told The Post.

Suffolk County Democratic Party Chairman Rich Schaffer was reelected to the top party post last month despite being hit with accusations that he tried to strong-arm party members and even offered money to some if they voted for him to keep the crown after 26 years as top dog.

The FBI declined to comment, but several party members and local government officials said they had been contacted by federal agents to discuss the Dem boss.

Multiple Democrats and former allies of Schaffer unleashed allegations of a Mafia-style pressure campaign that included backdoor deals with the local GOP to keep Dems off the county ballot to allow Republicans to run unopposed. 

They accused the 26-year chairman of threatening to get committee members fired from party-controlled jobs and even offering cash to those who would back him over progressive challenger Kathryn Casey Quigley in the party’s bitter civil war.

Schaffer offered payments to at least three different committee members in exchange for their attendance and vote, according to text messages reviewed by The Post.

“Can we pay him to miss work?” Schaffer allegedly texted one member about getting his father to skip his night shift as a security guard and instead come vote for him, according to messages viewed and previously reported by The Post.

An ally of Schaffer can also be heard pressuring committee members to fall in line with the boss or lose their jobs, according to audio obtained that was secretly taped at a meeting in the party headquarters prior to last month’s election.

Islip Town Democratic Chairwoman Leigh-Ann Barde, who said she once considered Schaffer her “political father figure,” turned on him after he allegedly threatened her husband Roc Romain on the secret tape. 

Romain is a committee member who holds a job at the Suffolk County Board of Elections.

Schaffer called the allegations against him “baseless” and said he had not been contacted by law enforcement as of Wednesday.

“Anyone that knows the reality of Long Island politics understands that Rich Schaffer is the model of professionalism and ethics,” his attorney Mark Lesko said. “We are confident in the facts and will not give these politically motivated allegations any credence.”

The New York State Attorney General’s office previously confirmed it was reviewing the whistleblower complaints against Schaffer.