Chris Christie once ordered ex-Port Authority executive Bill Baroni to curse out one of his critics — or risk losing his job, it was revealed Tuesday at the Bridgegate trial.

Under cross-examination, Baroni told Newark federal jurors that he received a call from the governor while he was on the way to his teaching job at Seton Hall Law School.

“’Bill, we need to do something,’” Baroni quoted Christie.

Then Christie ordered Baroni to call Bill Lavin, president of the NJ Firefighters Mutual Benevolent Association, “and tell him to go F himself,” Baroni testified.

Lavin had recently criticized the governor on the radio.

When he balked, Christie threatened his position as deputy executive of the Port Authority, asking, “Do you like your job?”

“He knew I was Bill Lavin’s friend, and he threatened my job if I didn’t do it,” he testified.

“And you did it?” Assistant U.S. Attorney Lee Cortes asked.

“Yes,” Baroni said.

Lavin called it an “unforgettable” conversation.

“I was disappointed,” he told The Post by phone. “Not so much from the governor, I knew he was a soulless individual. But I was disappointed with Bill Baroni. I thought he would be above that.”

“The governor has proven himself time and time again to be a fraud and just a person of very low character,” he added.

On Tuesday, prosecutors sought to show that Baroni was Christie’s “attack dog” who had an incentive to follow through on orders of political retaliation from the governor.

Baroni and ex-Christie aide Bridget Anne Kelly stand accused of blocking off lanes leading to the George Washington Bridge in order to create a traffic jam that would punish Fort Lee Mayor Mayor Sokolich for not backing the governor’s re-election.

On Monday, Baroni had insisted that he thought he was closing entrance lanes on the bridge as part of a traffic study — not to get back at the mayor.

He said the only reason his didn’t return increasingly desperate messages from Sokolich was because he was ordered not to by the government’s star witness David Wildstein.

Cortes also asked Baroni about a time when he embarrassed the late Sen, Frank Lautenberg at a meeting about toll hikes — at the governor’s behest.

Lautenberg objected to the hikes, prompting Baroni to waive a PA-issued E-ZPass that allowed Lautenberg to avoid paying tolls for years.

Baroni then argued that it was “impossible” for Lautenberg “to argue fairness for tolls” he didn’t pay for, Baroni said.

“Gov. Christie was thrilled with your performance wasn’t he?” Cortes asked.

“He was not unhappy,” Baroni said.

“He called you an attack dog, didn’t he?” Cortes asked.

Baroni denied that, but later said he “felt badly” about attacking Lautenberg because he didn’t “like being the attack dog.”