The rule is part of recent legislation regulating working from home, a practice that has exploded since the start of the pandemic.
Under the new legislation, employers are also responsible for providing workers with the appropriate tools to make it possible for them to work remotely, and they must reimburse the workers for any increase in bills such as electricity or gas brought on by working from home.
Portuguese employees can now also opt out of remote working if they want - but also request to work from home if their job allows them to do so.
In 2017, France also gave workers the right to ignore all after-hours emails from their bosses.
Tech research company Gartner estimates that remote workers will represent 32 per cent of the global workforce by the end of 2021, compared to 17 per cent in 2019. This increase has been blamed on the Covid pandemic.