The memo, circulated by the provincial commissioner on September 15th, referred to the attire of officers when attending court, according to Spanish daily El Diario.
It provoked furious responses. One officer complained, "They've directly called us pigs!"
Gonzalo de Miguel, spokesperson for the Unified Police Union (SUP) in Zaragoza replied, "They've never said anything in court. And we go there every day."
A police spokesperson told reporters that the memo was "a simple reminder about decorum".
"It encourages officers to present themselves properly groomed and dressed. In a jacket and tie, if possible."
But De Miguel claimed that it was "an outrage to say that one could be confused with another because of physical appearance. Officers identify themselves immediately with their official badge."
De Miguel added, "It's gone down very badly in the force, as you'd expect. Because what it says is that officers lack cleanliness and that's completely untrue."
The union has demanded a meeting with the commissioner to ask for the memo to be rectified.
"He's tried to clarify it by saying that his only intention was that they should dress decently. It's an untrue and incorrect value judgement."
De Miguel implied that the lack of experience of the commissioner may have played a part in the communications breakdown.
"He's very new in the job," he said.