Amsterdam fire chief Leen Schaap was appointed to tackle "white male culture" in the fire brigade, and is now facing death threats.
Dutch prosecutors have opened an investigation, amid reports that the threats come from his own staff.
Mr Schaap was brought in from the police in 2016 but now needs extra security, AD newspaper reports.
Money was raised to have him knocked over by a car, it alleges, while another threat came from a biker gang.
Mr Schaap has not spoken directly about the threats.
But the city's new mayor, Femke Halsema, said she had discussed the "unacceptable" situation with him and promised to treat the fire brigade affair as a priority.
Leen Schaap was appointed to stamp out what late Mayor Eberhard van der Laan described as a "closed culture in which racism, discrimination and bullying take place".
But Mr Schaap angered serving and retired firefighters when he spoke publicly about the problems he faced in recruiting more women and immigrants.
He suggested the organisation had an internal code in which workers refused to betray their colleagues, and he criticised the shift system in which firefighters did not have to turn up for work on 270 days in a year and were able to have second or even third jobs.
"Enough of this man," wrote one person on Facebook, beside an image of a sheep torn into pieces, AD reported. The fire chief's surname means sheep in Dutch.
Several unions also criticised Mr Schaap and called for him to face an investigation for dereliction of duty.
When asked about the hatred that he had encountered in his reform drive, he said last May: "I'm not a baby and I'm pretty used to it in the police. This affects me but doesn't infect me."
A number of firefighters have been questioned in connection with the threats but no arrests have been made.