A father-son team of city marshals hauled in a record $6.8 million in fees last year in part because there are only 39 of the mayor-appointed debt collectors to cover the entire city, The Post has learned.

As many as 83 marshals — who go after everyone from parking scofflaws to judgment deadbeats — are allowed under the law. But Mayor de Blasio hasn’t appointed a single new one since taking office 18 months ago and has yet to get around to reorganizing a screening committee to vet 27 people who applied for the lucrative job during that period.

That’s given the current crop of marshals a clear field to stalk deadbeats and pocket 5 percent of the proceeds, plus additional fees.

Leading the pack was veteran Martin Bienstock with revenues of $5.1 million. Records show that his son, Gregg, ranked fifth with earnings of $1.7 million working out of same Bayside, Queens office as his dad.

The Bienstocks aren’t the only marshals who operate as a family business.

George Essock Sr. and son George Jr. also work together out of a Bayside office, while brothers Jeffrey and Gary Rose work out of Brooklyn.

Michael Woloz, a spokesman for the Marshals Association of New York City, said the group “wants to see the mayor” reconstitute the selection committee to “assess the need for new marshals” but has “no opinion” on whether more marshals should actually be hired.

Monica Klein, a de Blasio spokeswoman, said the city “is in the process of appointing a marshal selection committee made up of members who represent our city’s diverse communities and who will choose qualified marshal candidates.”

The Bienstocks are a lot more than a pop-and-son operation. They employ 23 workers, have a long list of high-end corporate clients and also collect on behalf of the city’s Department of Finance and state Attorney General’s Office.

They make their millions collecting court judgments, seizing properties and putting the squeeze on paychecks and bank accounts of deadbeats.

Unlike most other marshals, they don’t boot and tow parking scofflaws.