A former 15-term New York City congressman is a “sexual predator” who allegedly violated a teen at an upstate Boy Scout camp, according to a shocking lawsuit filed last week naming the life-long Democrat.

More than a decade before Gary Ackerman, 76, was first elected to Congress, he worked as a camp director when the lurid incident allegedly took place on an abandoned road within the sprawling, 12,000-acre Ten Mile River Camp property near Narrowsburg.

The anonymous victim was 17 in August, 1966 when, he claims in Manhattan Supreme Court papers, Ackerman manipulated him into taking a ride. Once secluded on the back road, Ackerman, who was 23-years-old at the time, is accused of trying to touch and fondle the teen before forcing oral sex, the victim charges.

The legal filing identifies Ackerman as a “known predator” whom the Boy Scouts “should have known” had the potential to harm kids.

The Boy Scouts said they had no record of abuse allegations against Ackerman.

Ackerman, known for his white carnation boutonniere and the 1966 Plymouth Valiant he drove while working on Capitol Hill, went on to represent parts of Queens and Long Island in the US House of Representatives, before retiring unexpectedly in 2012.

Calling the “highly respected” Ackerman a predator is “especially offensive” and nothing less than slander, his lawyer, Oscar Michelen, told The Post.

The alleged incident never happened, the attorney insisted.

“He denies any such incident took place,” Michelen said, noting the married father of three has led “an impeccable life” and “was and is a beloved and admired public servant.”

“He denies any wrongdoing whatsoever. How come no such thing ever came up at any time — not at Ten Mile River, not with the Boy Scouts and not in 36 years of public life?”

The lawyer said. “It’s shocking. It’s outrageous and completely opposite of the person everyone knows Congressman Ackerman to be.

“We obviously intend to vigorously defend the Congressman’s honor and reputation in this case. We’re confident he’ll be vindicated.”

New York’s recently enacted Child Victim’s Act gave the victim — now 70 — the chance to come forward, his lawyer, Jordan Merson, explained.

“He did not have a legal basis to file a claim, and now he does,” Merson said. “He’s not doing this for publicity, he’s doing this because he feels he was wronged, and taken advantage of, and he wants to have his opportunity to have his day in court.”

Whenever the once prominent Ackerman appeared on the television, the victim “felt like he was trapped in that car again,” Merson said. “He goes immediately into PTSD symptoms, and anxiety, every time he sees or hears [Ackerman’s] name. He goes into a panic attack.”

“Our allegation is that the Boy Scouts either knew or should have known that Ackerman would do this, or would have the propensity to do this, that’s what we intend to do by and through discovery,” the victim’s attorney added.

More than 500 Child Victim Act lawsuits have been filed across New York State since the law’s “look back” window opened Aug. 14, giving victims whose claims were previously barred by the statute of limitations a one year period in which to bring legal claims.

The legislation also changed the statute of limitations to allow victims to bring court cases until they are 55 years old, instead of just 23.

Ackerman served on the House Financial Services and Foreign Affairs committees, was a champion of Israel and was the ranking Dem on the Middle East and South Asia subcommittee. In 1996 he helped pass a law requiring hospitals to inform mothers when their newborns tested positive for HIV.

In 2010, the co-signed a letter with two dozen members of Congress urging the Boy Scouts to stop discriminating against LGBTQ parents.

“I’ll always be a proud Eagle Scout, but this discriminatory policy must end,” Ackerman said in a statement at the time. “Rejecting a Cub Scout’s mothers from volunteering just because of their sexual orientation doesn’t comply with the Scout law I recited at Scout meetings.”