The cadets have been informed of this so-called soft recommendation in light of the shootings of two police officers Saturday, which police commissioner Bill Bratton described as "assassinations."
Officials described the move as a common-sense precautionary step because they have also been assessing a number of copycat threats since the initial attack.
Former Det. Sgt. Joe Giacalone, who spent one of his 21 years on the force training cadets directly, said many of the police academy cadets normally wear their uniforms to and from work but they, unlike full-time officers, are unarmed.
"It doesn't matter who is wearing the uniform. It's the uniform itself [that] is the target," Giacalone told ABC News.
"The police department, because it's under siege, has to worry about protecting their own lives first."
It's not just cadets in uniform who have to worry about being associated with the NYPD, Giacalone said, because NYPD T-shirts and hats are regularly worn by those not on the force.
Giacalone said he told his father, who he said regularly wears an NYPD baseball hat to support his son, to keep the hat in the closet for the time being.
"I don't want anybody taking a potshot ... and his only relationship is that he's my father," Giacalone said.
The dress-code warning is not the only precaution the NYPD is taking today. Auxiliary officers, who are unarmed, are not being used until further notice, and every patrol has been assigned two officers.
The latter directive largely applies to foot patrols, now meaning that officers will go out in pairs when on those shifts.