Employers can read workers' private messages sent via chat software and webmail accounts during working hours, judges have ruled.
The European Court of Human Rights (ECHR) said a firm that read a worker's Yahoo Messenger chats sent while he was at work was within its rights.
Judges said he had breached the company's rules and that his employer had a right to check on his activities.
Such policies must also protect workers against unfettered snooping, they said.
The judges, sitting in the ECHR in Strasbourg, handed down their decision on Tuesday. Countries that have ratified the European Convention on Human Rights, which include Britain, have agreed to abide by the ECHR rulings that involve them.
The impact on domestic courts differs. Under UK human rights laws, judges must take into account the ECHR's decisions but are not bound by them.