The Supreme Court has ruled that employers may monitor employee conversations made via an employer-issued cell phone if there is a “legitimate work-related purpose” to do so.

In a ruling handed down Thursday, the court ruled unanimously that a police department in California did not violate privacy rights by monitoring text messages of an employee sent on a department-issued device.

A review of the messages of SWAT team officer Sgt. Jeff Quon after he exceeded his monthly service limits revealed personal and sexually explicit texts to both his wife and his mistress.

The police department of the city of Ontario conducted the review as part of an investigation into whether a character limit on the city’s contract with a company called Arch Wireless was “sufficient to meet the City’s needs,” according to the ruling.

Quon argued that the review violated his Fourth Amendment right to privacy, but the Supreme Court disagreed.

“Reviewing the transcripts was reasonable because it was an efficient and expedient way to determine whether Quon’s overages were the result of work-related messaging or personal use,” the Court’s opinion stated.

Officers at the police department were told that a certain amount of personal use on the devices was allowed, but that they should not expect total privacy because messages were all subject to auditing.

The ruling reversed ones in Quon’s favor by a district judge and the U.S. Court of Appeals for the 9th Circuit. It also sets a precedent for allowing employers to monitor cell-phone of employees if they feel they have just cause.

Still, the Court made it clear in its decision that it would make future decisions on a case-by-case basis and would exercise caution before giving employers blanket license to review such messages in the future.

“The Court must proceed with care when considering the whole concept of privacy expectations in communications made on electronic equipment owned by a government employer,” according to the opinion. “The judiciary risks error by elaborating too fully on the Fourth Amendment implications of emerging technology before its role in society has become clear.”