A University of Sydney recruiting campaign that inferred people who are not white were "criminals" has fallen foul of the advertising watchdog.

Thirteen "Unlearn criminal" billboards appeared at train stations across Sydney depicting a young woman of colour gripping a fence with the words written over the top.

The University of Sydney argued its campaign promoted the "critical thinking skills" that allow students "to question established beliefs and to think critically in order to foster a positive change in the world".

According to a complainant, the billboard was offensive "particularly given the over representation of Aboriginal and Torres Strait Islander women in our prison system".

"These women make up around 34 per cent of the female prison population but only two per cent of the adult female population," the complainant said.