Ms Fitzgerald delivered the message at a ceremony marking the beginning of training for 100 recruits at the training college in Templemore, Co Tipperary, which last saw graduates leave in 2011 due to the financial crisis.
The minister said officers needed courage to challenge bad conduct within the force.
“Courage is called for without any physical threat. Courage can be called for in the middle of a quite normal day. The courage to say ‘No’ if you believe the instruction is wrong. The courage to cry halt to a practice that may have been going on forever, but that should stop right there and then.”
Her comments came after the force was rocked by a number of controversies including widespread quashing of penalty points, and a raft of allegations by whistleblowers.
Ms Fitzgerald said the introduction of a new DNA database will “help transform serious crime investigations and deter criminals”.
After a four-year recruitment freeze which was only broken last year, Taoiseach Enda Kenny said the Government was committed to providing more resources for policing. “That’s why we opened up this college. It won’t close again.”