A New Jersey state senator is demanding that authorities investigate a corruption-watchdog commissioner who was hired by a law firm after it had landed work with the honcho’s agency.

Waterfront Commission co-head Ronald Goldstock, was hired by the Chicago-based Pugh, Jones & Johnson firm after his bi-state agency selected it as one of several firms on a short list of independent private monitors.

Pugh got the job from the anti-corruption head in 2013 — and the next year, Goldstock was hired by the firm.

After The Post exclusively reported the alleged conflict of interest, New Jersey state Sen. Ray Lesniak (D-Elizabeth) demanded that US Attorneys Preet Bharara and Paul Fishman, as well as New Jersey Attorney General Chris Porrino, open a probe into the matter.

“I am asking that you all coordinate and open an investigation into Commissioner Goldstock’s relationship with Pugh, Jones & Johnson and his role as a Waterfront Commissioner,” Lesniak wrote to them in a letter dated Oct. 5.

“Such egregious conflicts and self-dealing should never go uninvestigated, unchallenged or unpunished, when warranted.”

Phoebe Sorial, a commission lawyer, said Lesniak was “politically motivated,’’ adding that Goldstock had nothing to do with taking on Pugh.