A new report finds that the city's Department of Correction has been misusing city cars. NY1's Dean Meminger filed the following report.

Correction Commissioner Joseph Ponte has been hitting the highway big time in his city-issued SUV. But the Department of Investigation says all that mileage had nothing to do with running city jails. 

"Commissioner Ponte misused his vehicle," said Mark Peters, commissioner of the Department of Investigation. "He took it for trips on vacation. He took it to trips to Maine. He took it to resorts."

DOI found that Ponte and his senior staff were the department's worst violators of rules banning the use of city vehicles for personal travel. 

A total of 21 department officials misused their vehicles, costing taxpayers more than $20,000.

"Over 250 trips," Peters said. "To Niagara Falls, to casinos, to social events in Washington D.C. It cannot be allowed to continue."

After an anonymous tip, DOI examined data from GPS devices and E-ZPasses in each vehicle, and gas charges. It found Ponte's vehicle was outside the state on 90 days in 2016, about a quarter of the year, a lot of that time in Coastal Maine.

"You cannot bring order and safety to the city's jails and insist that the corrections officers follow the rules when you aren't following the rules yourself," Peters said.

Mayor Bill de Blasio says city employees will be retrained in the use of city vehicles, but that he's supporting Ponte. 

"Commissioner Ponte, to the best of my understanding, was told by his own internal staff this was the right way to handle things," de Blasio said. "He is someone who is on call 24 hours a day."

But DOI said the mayor was wrong. The investigation found Ponte and his staff were never given such official advice.

"It is not good for the efficient running of government and for government integrity to try to defend these kinds of actions," Peters said.

The correction department said if any rules were broken, it was by mistake.

DOI is referring its investigation to the proper "enforcement authorities." 

The correction officers' union, which has been battling the commissioner over how to reduce violence on Rikers Island, says the commissioner should resign immediately.