The Strasbourg-based European Court of Human Rights (ECHR) ruled Tuesday that a Romanian man should not have been fired for sending private messages at work, overturning a decision by a Romanian court on the matter.
Bogdan Mihai Barbulescu was sacked for sending the messages via the Yahoo messaging system in 2007. His employer had used surveillance software to monitor his computer activity.
A Romanian court ruled in 2016 that the firm was within its rights but this has now been overturned after Mr Barbulescu successfully challenged the original decision.
Some of the communications he had sent were "intimate in nature" and were sent to his brother and fiancee, the court heard.However, his right to privacy had not been "adequately protected", the ECHR has now ruled.
The ECHR also added it was not clear whether Mr Barbulescu had been warned that his communications would be monitored, and that the original court had not established specifically why the monitoring had taken place.
As ithe ECHR is the highest court, there can be no further appeal.