Saying taxpayers shouldn’t be stuck with the bill for $13.6 million in legal fees to defend against City Hall corruption investigations, a new lawsuit seeks to force Mayor de Blasio and several top aides to pay their own way.

The suit, electronically filed on Sunday, alleges that de Blasio and his “underlings” engaged in “criminal and/or unethical behavior…outside the scope of public employment and thus should not be covered by the city of New York.”

In addition to forcing de Blasio and the others to pay back the cash drained from city coffers, the Manhattan Supreme Court filing seeks unspecified punitive and “consequential” damages, plus the costs of litigating the case.

The court papers, obtained by The Post, note that “the ‘ethically challenged’ de Blasio” broke a February 2017 promise that no public money would “fund the mayor’s individual compliance” with the pay-to-play probes — and that he made a “quiet statement” revealing his about-face “on the Friday ‘getaway day’ before this year’s Fourth of July weekend.”

Other defendants targeted by the Manhattan Supreme Court suit include top City Hall aide Emma Wolfe, former de Blasio fund-raiser Ross Offinger and former mayoral consultant Josh Gold, although court papers suggest there are additional, “as yet unknown co-conspirators who came under investigation.”

Lead plaintiff and Democratic mayoral challenger Sal Albanese said he and his fellow plaintiffs — Guardian Angels founder Curtis Sliwa and Staten Island political activist Frank Morano — plan to unveil the suit at a Monday news conference outside of the former Tweed Courthouse in Lower Manhattan.

“We’re doing it in front of the Tweed Courthouse because it symbolizes municipal corruption,” said Albanese, a former Brooklyn city councilman.]

“What the de Blasio administration has engaged is in pay-to-play politics on steroids.”

Sliwa said de Blasio could have easily paid his own $2 million in legal bills by mortgaging his two Park Slope properties in Brooklyn, and called his flip-flop on the issue “like taking a shiv and stabbing the people right in the back.”

“This is the worst treachery — and he’s been very treacherous over the past four years,” Sliwa said.

Exhibits attached to the filing include several Post reports, including a Friday exclusive that revealed the extraordinary influence wielded by two top de Blasio campaign contributors, one of whom, Jona Rechnitz, has pleaded guilty to making political donations and paying off law-enforcement officials in exchange for favorable treatment.

De Blasio has claimed he barely knew either man, yet Rechnitz directly emailed de Blasio seeking an appointment to help “combat police corruption,” while the other man, Jeremy Reichberg, reached out to the first deputy mayor’s chief of staff about a water bill that got reduced from $650,000 to $125,304 due to what officials have said was a faulty meter.

The communications were contained in emails sought by The Post through the state Freedom of Information Law, and which were released by City Hall late Friday afternoon.

Sunday’s suit also contrasts de Blasio’s demand that taxpayers foot his $2 million in legal bills with the stance taken by scandal-scarred ex-President Bill Clinton and Hillary Clinton, who left with White House with $10 million in debts, “much of which was due to LEGAL BILLS.”

“The Clintons recognized that public taxpayer funds could not be used to cover litigation surrounding non-government activity such as Whitewater or the Monica Lewinksy scandal,” court papers say.

“A long-time supporter of the Clintons, de Blasio has evidently learned little from Bill and Hillary and their appreciation for middle class struggles.”

Both the Manhattan US Attorney’s Office and the Manhattan District Attorney’s Office closed their investigations of the de Blasio administration without bringing charges, but Manhattan DA Cyrus Vance Jr. issued a stinging statement that criticized the mayor’s fund-raising practices as appearing “contrary to the intent and spirit of the law.”

Albanese called paying the lawyers for de Blasio and his aides a “raid on the public treasury” because “most of the activity these people were investigated for was political in nature. It was not what taxpayers expect officials to be engaged in.”

Albanese, a lawyer, said the city often refused to indemnify public workers for actions taken “outside the scope of their employment,” and cited a case he handled on behalf of two security guards at an Upper Manhattan homeless shelter.

A resident who attacked a guard sued over “very fuzzy” allegations that he was subdued with a chokehold, Albansese said, and the guards’ union “had to shell out a lot of money in legal bills to compensate for the city not paying.”

De Blasio spokesman Eric Phillips said: “The public will only pay for legal fees associated with government work. Any personal or political legal work done for the mayor or aides won’t be paid for by taxpayers.”

“To say this suit is frivolous would be giving it too much legitimacy,” he added.

Additional reporting by Michael Gartland