A top New York labor leader and Gov. Cuomo ally has “extensive ties to organized crime,” federal prosecutors claimed Monday.

James Cahill, the former president of the New York State Building and Construction Trades Council, represented over 200,000 unionized construction workers until his arrest in October on bribery charges along with 10 other current and former members of Local 638. In a new filing, prosecutors say the feds were watching as Cahill met with members of the Gambino crime family and Serbian gangsters.

Cahill, 71, described himself as “the last of the Westies,” referring to an Irish-American crime family based in Hell’s Kitchen that once corrupted the construction industry, prosecutors wrote.

“Cahill has deep ties to leading members of organized crime who are known to engage in acts of violence and intimidation, which poses a threat to potential witnesses in this case,” Assistant U.S. Attorney Jason Swergold wrote.

In 2017, Cuomo called Cahill “a good friend to me and my entire family for so long.”

The indictment against Cahill does not mention Cuomo or feature allegations involving state development projects.

Linda Lacewell, the superintendent of the State Department of Financial Services and Cuomo’s former chief of staff, yelled at a Daily News reporter that it is borderline libelous to mention Cuomo’s ties to Cahill. She said The News should note every other politician Cahill has associated with in his long history as a labor leader.

“These allegations are ugly, disturbing and a slap in the face to the hardworking men and women who are part of the union movement. Anyone who breaks the law needs to be held responsible for their actions,” senior Cuomo adviser Rich Azzopardi said.

The six-page filing opposing Cahill’s request for more lenient bail conditions reveals that the labor leader, who appeared alongside Cuomo at announcements for major infrastructure projects like the new Mario M. Cuomo Bridge, was also allegedly rubbing elbows with hardcore gangsters.

Cahill was under surveillance as he met with Louis Filippelli, a capo in the Gambino crime family, according to the filing.

A recorded conversation on March 13 featured Cahill regaling a source cooperating with the government about decades-long ties to the Westies, the Gambinos and a Serbian organized crime family called Grupo Amerika, prosecutors claimed.

“John (Gotti) was like this with my brother and brother-in-law and this guy, Bosko. That was his crew. That was his Irish crew,” Cahill allegedly told the source cooperating with the government on March 13.

Cahill was referring to his brother Mickey Cahill — an alleged member of the Westies — his brother-in-law Buddy Leahy, and Bosko Radonjic, the former head of the Westies, prosecutors wrote.

Radonjic fled the U.S. in 1992 and died in Serbia in 2011. In the conversation, Cahill described Radonjic’s “understudy” as a gangster named “Michael Michael.”

Prosecutors identified “Michael Michael” as Mileta Miljanic, the reputed leader of Grupo Amerika.

“He’s my guy,” Cahill allegedly said of Miljanic.

Cahill’s attorney Sam Talkin denied the charges.

“Mr. Cahill denies he has any association with organized crime,” Talkin said. “The Westies have been defunct for three decades. And John Gotti has been dead for nearly two decades. That sums up the accuracy of the government’s allegations.”

During the same alarming conversation, Cahill allegedly said Miljanic was part of a “mass murdering crew.” Cahill boasted that he’d personally intervened after his nephew received a death threat from Miljanic, prosecutors wrote.

“If you bother him, I’m gonna go away from yous, I won’t talk to yous, I’m done,” Cahill said in the recorded conversation.

The feds say they were also spying as Cahill met with Miljanic “on numerous occasions.”

The bribery scheme allegedly earned Cahill and his cronies over $100,000 since Oct. 2018. The indictment claims that Cahill accepted bribes from the cooperating source, who was a non-union employer. In exchange, Cahill pledged to use his influence to make sure the employer was not hassled for using non-union labor on a project in Nassau County, prosecutors charge.

“If you become union, you’ll have 12 f--king guys on your back,” Cahill allegedly told the source in Oct. 2019 after taking a bribe.

“Welcome to the real world.”