Former New York City Mayor Bill de Blasio was hit with the largest-ever fine ever issued by the city’s watchdog group on Thursday for misusing government resources during his failed bid for the White House in 2019.

The Conflicts of Interest Board ordered de Blasio to cut taxpayers a check for nearly half-a-million dollars — $155,000 fine as punishment; plus another $320,000 to reimburse the treasury for the expenses the NYPD incurred as the security detail accompanied him around the country.

The fine comes more than a year after de Blasio was excoriated by a Department of Investigation report that detailed his extensive use of his security detail during his presidential campaign, revealed that he had done it against ethics guidance and said it amounted to using government resources for political purposes.

“The Conflicts of Interest Board’s conclusions regarding former Mayor Bill de Blasio’s misuse of his security detail reaffirms DOI’s investigative findings, and shows that public officials — including the most senior — will be held accountable when they violate the rules,” said DOI commissioner Jocelyn Strauber, in a statement.

De Blasio’s presidential campaign lasted for just four months and he never rose above one or two percentage points in the polls in the 2020 Democratic primary, which was eventually won by President Joe Biden.

Attorneys for de Blasio quickly filed a lawsuit in Manhattan Supreme Court to block the fine and accused the ethics watchdog of endangering public officials.

“In a time of unprecedented threats of political violence, the COIB’s reckless and arbitrary ruling threatens the safety and security of our democratically-elected public servants,” said de Blasio’s lawyer Andrew Celli.