Manhattan’s largest development company says it was snookered into paying union workers $42 an hour — and a lot more for overtime — just to deliver coffee at its Hudson Yards megaproject.

The “coffee boys” were part of what Related Cos. calls a widespread scheme of “misconduct” by unions that inflated construction costs at the gleaming new mini-city by more than $100 million.

While the job of coffee boy is usually filled by “the junior-most worker in a unit,” the Concrete Workers District Council assigned that role to two full-fledged union members, according to a Manhattan Supreme Court lawsuit filed Monday by Related subsidiary Hudson Yards Construction LLC.

One of the workers — identified as “Coffee Boy #1” — also happens to be “the 55-year-old brother of a high-ranking union official,” the suit says.

Adding insult to injury, the concrete workers’ coffee boys — who are paid $42.48 an hour, plus $27.39 worth of benefits — actually charge their colleagues for beverages and food, meaning that “although categorized as employees, they are actually vendors,” according to the suit.

“In the month of February 2015 alone, for the privilege of selling coffee and snacks at the Project, Coffee Boy #1 was compensated for 155 hours work, of which 45 hours were classified as overtime payable at time and a half or $69.87 per hour including benefits,” the lawsuit charges.

Time and a half on $42.48 an hour is $63.72, and it’s unclear why that amount isn’t reflected in the overtime calculation.

The alleged coffee boy scheme was cited in the lawsuit against the Building and Construction Trades Council of Greater New York, an umbrella group for the unions, and its president, Gary LaBarbera.

Court papers accuse the council and LaBarbera of “condoning, if not actively participating in, various corrupt practices” at Hudson Yards that violate a labor agreement they championed on behalf of 35 unions working at the site.

Other allegations in the lawsuit include widespread time-sheet fraud through which one construction worker raked in more than $600,000 in annual wages and benefits. The unidentified hardhat allegedly claimed to have worked 12 hours a day and seven days a week for an entire year.

Other workers typically inflate their hours by 10 to 20 percent, court papers claim.

The suit doesn’t seek damages for the alleged corruption, but says it justified Hudson Yards Construction in declaring that the office tower at 50 Hudson Yards would be a “merit shop” project for which contracts would be awarded “irrespective of whether the bidder used union or non-union workers.”

The suit accuses the council and LaBarbera of “tortious interference with prospective economic advantage” involving that project on grounds that they’ve encouraged some unions to not work at the site.

Hudson Yards Construction is seeking at least $75 million in damages on that claim, along with at least $200,000 from LaBarbera for allegedly defaming the company.

The suit alleges that LaBarbera was behind fliers that call Hudson Yards Construction “union busters” and also cites remarks he made during a Nov. 14 protest rally where he told workers the company wants to “use you up and throw you to the side.”

A spokesperson for the BCTC said, “We have not seen the lawsuit so we cannot comment. This is likely a retaliatory response to a movement in New York City, known as #CountMeIn, protesting open shop and non-union development.”​​