The public service union Unison says that Susan Shine, 35, an occupational health nurse who worked for Cleveland police authority, was providing medicines in the same way as "tens of thousands" of her colleagues every day all over the country.
While there is a degree of latitude over nurses' use of drugs, there is considerable confusion over what is allowed.
The United Kingdom Central Council for Nursing, Midwifery and Health Visiting (UKCC) "cautioned" Ms Shine for giving vaccinations, antibiotics and painkillers to police officers, despite a decision by the Crown Prosecution Service that a prosecution would not have been "in the public interest".
Unison wants a meeting with Frank Dobson, Secretary of State for Health, in an attempt to clear up the confusion.
Bob Abberley, head of health at the union, said that unless the situation was clarified, his organisation would advise its nursing members to refuse to administer medicines without the authority of a doctor. The union is also considering legal action against the authority.
If nurses refused to prescribe drugs it could lead to problems in key areas of public health when nursing staff are often forced to operate without the supervision of doctors.
Mr Abberley claimed the reference to the UKCC, a statutory professional body, had followed a complaint of sexual discrimination by Ms Shine.
The union official said that Ms Shine had vaccinated police officers against hepatitis B after they were bitten by suspects and had also administered painkillers to patients.
"There is no question that she is a first-class nurse and there has never been any accusation that there were any ill-effects from her work. It is custom and practice all over the country for nursing staff to administer the kind of drugs prescribed by Ms Shine."
A spokesman for the UKCC said that only nurses with special training or in designated areas were allowed to give certain medicines and Ms Shine was in neither category.
The Royal College of Nursing said that technically the body was correct but the law had not caught up with nursing practice. Although the "caution" would stay on her record for five years, it was the most lenient penalty open to the UKCC.