The Garda Representative Association said this could be taken as “encouragement to indiscipline” or construed as “licence to mutiny”.

PJ Stone, GRA general secretary, said that such a directive to new gardaí could “only end in trouble”. He was responding to comments made earlier this month by Ms Fitzgerald to 100 recruits on their first day at the Garda College, Templemore.

“When we think of the courage that gardaí need to show, we automatically think of the days when a gun is turned on you, a knife is raised at you or a car is driven at you,” she told students. “But courage is also called for when there is no physical threat. Courage can be called for in the middle of a very 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 for ever, but that should stop right there and then.”

In his editorial in Garda Review, the GRA official journal, Mr Stone said people were expecting a lot of things with the “sea change” promised by Ms Fitzgerald.

“What we were not expecting was the Minister for Justice encouraging trainee gardaí to say ‘no’ to instructions if they ‘believe the instruction is wrong’,” he said. “This could be regarded as encouragement to indiscipline or construed as licence to mutiny by these words from such a senior and experienced politician taken at face value.

“Surely the minister was not undermining the pyramid structure of rank within a disciplined force?”

He said protocols and protections outlined in law covered whistleblowing, and added: “But no such whistleblowing policy covers a junior garda for saying ‘No’ to a lawful instruction given by a senior rank — this can only end in trouble.”