The Port Authority is no longer running criminal background checks on businesses applying to operate at area airports — a policy that critics say will welcome back the Mafia, The Post has learned.

The astonishing change began nearly four months ago when the PA quietly ditched its long-standing corruption-fighting tool that required background checks on new businesses and their principals before they could operate at JFK, La Guardia, or Newark airports, a source explained.

“This will lead to bad outcomes. It’s an open invitation for organized crime figures to once again do business at our airports,” one insider said.

The checks, implemented about 25 years ago to weed out mob-owned businesses, were performed by a PA lieutenant and several detectives who carefully reviewed paperwork and conducted in-person interviews on about 100 new companies annually.

Additionally, the screening called for existing firms and their senior executives to be “revetted” whenever their PA contracts were renewed.

Only about 5 percent of applicants were disqualified, but sources said the probes also had a “deterrent effect.”

“You can never measure how many vendors or officials simply didn’t apply [to work at the airports] because we did this,” said the source.

On Oct. 16, the PA police issued an internal memo abruptly canceling all vetting protocols.

“Such background checks are not required by applicable law or regulation. Accordingly, effective immediately, such background checks are hereby eliminated,” wrote PAPD Superintendent Michael A. Fedorko.

The policy change was ordered after businesses complained that the vetting process, which took anywhere from a few weeks to several months, had grown burdensome, a source explained.

The firms bellyached that background checks were “taking too long to complete,” the source added.

The protocols were adopted as a “best practice” meant to safeguard the integrity of airport businesses permitted to interact with millions of travelers each year.

The checks were meant to help loosen the mob’s stranglehold on area airports, a problem depicted in the 1990 movie, “Goodfellas,” which showed the powerful grip the Luchese crime family once exerted over JFK Airport.

Firms were required to submit incorporation papers, PA vendor contracts, a list of other airport firms with whom they did business, names and photos of senior executives and other paperwork.

PA detectives would then scour the documents and perform “due diligence” probes, combing data bases for terrorism links, mob ties, prior criminal histories, outstanding civil judgments, bankruptcies or suspiciously large debts that threatened the ability to deliver promised goods or services.

And finally, applicants were required to submit to in-person interviews so they could clear up any lingering suspicions that cropped up.

Those who passed muster not only won permission to work inside airports, but gained closer access to tarmacs or restricted areas, critics say.

The PA did not directly address charges that the decision had compromised security, but spokesman Steve Coleman said:

“Every employee and individual with unescorted access to the secure areas of the Port Authority’s airports undergoes a rigorous FBI and TSA background check and Security Threat Assessment.”