Texts and emails sent by public employees on their personal devices or accounts are a matter of public record if they deal with official business, the California Supreme Court ruled Thursday in a unanimous decision hailed by open-government advocates.

But the court provided only general guidance on where the line would be drawn, posing a challenge for cities and counties forced to balance employees' privacy against the public's right to know, reports the Los Angeles Times.

The court said that communications sent on personal cell phones and computers must be disclosed to the public if they "relate in some substantive way to the conduct of the public's business."

"A city employee's communications related to the conduct of public business do not cease to be public records just because they were sent or received using a personal account," Justice Carol A. Corrigan wrote for the court.

Local governments throughout the state have expressed concerns that broad requests for information would be costly and might invade the privacy rights of workers.

The court acknowledged those concerns, saying it would not always be clear whether a communication had to be disclosed.