Brooklyn Borough President Eric Adams violated city ethics laws while hitting up fat-cat donors to attend a major fundraiser last week — five years after being scolded by city investigators over the same thing.

The office of the borough president — and now presumptive mayoral candidate — sent out an e-mail blast to more than 23,000 people Sept. 16 asking them to attend Wednesday’s annual gala.

The event, hosted by actress Rosie Perez at the Brooklyn Museum, was for Adams’ One Brooklyn Fund, which, like Mayor Bill de Blasio’s now-shuttered nonprofit Campaign for One New York, has been the subject of multiple investigations.

Adams’ mailing list included reps from companies who have received work from or have other types of business relationships with the city, according to people invited to the fundraiser.

But while Adams received the blessing from the city Conflicts of Interest Board for his office to send out the e-mail, the missive lacked one key thing: a mandatory disclaimer warning prospective donors that any contribution “will not affect any business dealings with the city or provide special access to city officials.”

Adams’ fund made a similar error in 2014, according to a city Department of Investigations memo at the time. No penalties against him were ever issued.

When confronted by The Post about the latest violation, Adams spokesman Jonah Allen insisted that it was unintentional and blamed it on a Borough Hall computer error.

“Due to what appears to be a software glitch,” the disclaimer was “erroneously omitted, … and as such we are working with Borough Hall [Information Technology] staff to get to the inconsistent content management,” Allen said.

The rep forwarded The Post copies of three other similar e-mail blasts for the same event that included the required disclaimer. Those invites were sent out directly by One Brooklyn staff, not Borough Hall.

The COIB declined comment, but under the board’s rules, Adams could potentially face fines and other penalties over the omission.

Since being formed in 2014, One Brooklyn has raised $2.03 million in funds used to help sponsor summer concerts, senior events and other public programs — all of which heavily promote Adams.

Many of the nonprofit’s major donors have historically enjoyed close business relationships with both Brooklyn Borough Hall and City Hall. They include DUMBO-based developer David Walentas and his family, Barclays Center operator Brooklyn Sports & Entertainment and Broadway Stages, a Brooklyn-based firm questioned in the probes of de Blasio’s fundraising.

Adams, a former state senator and retired NYPD cop, asked guests to fork over $150 per plate — and VIPs $500 — for the fundraising dinner honoring “Cornerstone Brooklyn Businesses” who have been operating in the borough at least 50 years.

Corporate sponsors who helped pay for the event included several entities that also do business with the city, such as powerhouse developer Scott Rechler’s RXR Realty and National Grid.

Allen said 153 people attended the gala, raising $24,253. He said “a substantial number of free tickets” were given to people and groups “who couldn’t afford to pay.”

The Post in 2016 reported that One Brooklyn was the subject of two separate city Department of Investigation probes, and like de Blasio’s nonprofit, was also scrutinized by the feds to see whether it was used to dish out pay-to-play favors to donors.

In 2017, federal and state authorities dropped their probes into de Blasio’s fundraising efforts but still criticized his administration for violating the “intent and spirit” of election law.

DOI has twice investigated One Brooklyn and both times determined it was breaking city rules, although the nonprofit was not hit with any penalties.

Besides the 2014 case over improper fundraising, DOI in 2016 found One Brooklyn wrongly collected more than $95,000 in rental fees for Borough Hall events rather than have the payments go into the city coffers, records show. The money was ultimately given to the city.

DOI first began scrutinizing One Brooklyn after the Post reported in March 2014 that it was soliciting donations — even though it had yet to register with the state and technically had yet to exist.