Remember why unions were formed in the first place — to protect workers from being taken advantage of?

Nowadays, the rank-and-file mostly need protection from their own leadership.

Daniel Hughes, former head of the Field Supervisor Association representing Port Authority workers, pleaded guilty in Brooklyn federal court this week to looting $300,000 in members’ dues over five years.

The union heavyweight allegedly used the money for Queens hotel trysts with hookers, casino getaways and high-priced dinners.

A rare occurrence? Hardly.

Last May, ex-Central Labor Council boss and former Queens Assemblyman Brian McLaughlin was sentenced to 10 years for embezzlement — including from the electricians union he once ran.

Other examples abound. A not-exhaustive rap sheet — partly tracked by the DC-based National Legal and Policy Center — includes:

* Aug. 5, 2009: Michael Forde, ex-head of the city’s District Council of Carpenters, was hit with a 29-count indictment for taking bribes from members — in exchange for allowing them to avoid mandatory contributions to their pension funds. Forde beat similar charges several years before.

* Feb. 11, 2010: Anthony Rumore, ex-president of Scarsdale’s Teamsters Local 812, pleaded guilty in federal court to making false statements related to extorting free labor out of his membership.

* Feb. 16, 2010: Thomas Pokrywczynski, former secretary-treasurer of Buffalo-area Amalgamated Transit Union Local 1342, pleaded guilty in federal court to theft of $254,000 in union funds.

* Feb. 17, 2010: Melissa King, former benefits administrator of the “Sandhogs” tunnel-digging union, was indicted for embezzling some $40 million from three benefit funds she oversaw.

* April 21, 2010: Wayne Mitchell, ex-president of Communications Workers of America Local 14170 (representing mailroom workers), pleaded guilty in a Manhattan federal court to embezzling $200,000.

* April 23, 2010: Mitchell’s immediate successor, Larry DeAngelis, pleaded guilty to stealing $60,000 from the union.

* May 11, 2010: Peter Thomassen, assistant supervisor of the above-mentioned carpenters union, resigned after a report showed huge amounts of spending on lavish parties, junkets and steak dinners. An indictment is anticipated.

An epidemic?

So it would seem.

Rank-and-file members can be forgiven for suspecting that there’s something about organized labor that attracts leadership of a criminal bent.