The manner in which NSW Police officers arrested and humiliated two women in hijabs over an alleged unbuckled seatbelt was "appalling" and had the potential to undermine the entire force, critics say.

An independent police oversight body on Thursday found the two officers engaged in serious misconduct, saying both were presently "unfit for purpose" as police officers.

The highway patrol officers ran two red lights before activating their lights and sirens to stop a 24-year-old driver and her stepmother in April 2019.

During the incident, Officer 1 told the driver she would "have to be the most stupidest (sic) person I've ever met as a driver".