The father of a once-feared mob enforcer pleaded guilty to his own extortion plot Thursday and now faces 20 years in federal prison.

John J. Rainone, 83, admitted to U.S. District Judge Jorge Alonso that he helped shake down a businessman six years ago in Bartlett, once meeting the victim at a Dominick’s grocery store and warning that “nobody is going to give you a problem if you do the right thing.”

Rainone was quietly indicted in 2015 along with his 41-year-old grandson, who shares the same name. The younger Rainone pleaded guilty to the same scheme in October and agreed to cooperate with federal investigators, records show. The judge has yet to set a sentencing date for either man.

While the attempted extortion charge they pleaded guilty to carries a maximum prison sentence of 20 years, the elder Rainone is more likely to face about three years in prison. His grandson is likely to face the same if he continues to cooperate with the feds.

The men are the father and son of Mario Rainone, the former Outfit muscle once described as an “urban terrorist” by a judge. Prosecutors have accused Mario Rainone of using violence and threats to squeeze Outfit debtors, even threatening to chop off the heads of a restaurateur and his children if he wasn’t paid $200,000.

Fearing his associates in the Outfit were out to kill him, Mario Rainone once entered the federal witness-protection program only to change his mind when his mother’s porch was bombed. Mario Rainone is serving a 15-year prison sentence, but he is hoping for a reduction in prison time based on a change in the law, his defense attorney Joe “The Shark” Lopez said.

The younger John J. Rainone was sentenced in 2015 to 38 months in prison after he pleaded guilty to access device fraud and aggravated identity theft, records show.

Now grandfather and grandson have been caught up in the same scheme. They’ve admitted that, in August 2010, they told a businessman that a reputed Outfit leader wanted to be “taken care of” and demanded $10,000. The businessman refused to pay. The younger Rainone then told him in October 2010 that he had to pay $2,000 a month in “street tax” after the unnamed Outfit leader had gone to prison.

During a meeting at a Bartlett Dunkin’ Donuts, the younger Rainone told the businessman, “You’re going to have to pay.”

The two Rainones met the businessman at the Dominick’s later that month, where the older Rainone searched him for a recording device. He told the businessman that “nobody is going to give you a problem if you do the right thing” and then he demanded $5,000 a month. When the businessman asked if he could pay less, the elder Rainone said he’d have to check because “everybody answers to somebody.”

They met at the Dominick’s again the next day, where the elder Rainone said, “You’re going to have a little problem later on” if he didn’t pay $4,000 a month. The businessman agreed to make the payment Oct. 13, 2010, but the elder Rainone showed up at his business a day early and insisted on receiving the payment. The businessman refused.

The elder Rainone then said “they” were going to “send the rough guys to collect,” according to his grandson’s plea agreement.