At least 65,000 Belgian government civil official have got the right not to be contacted outside normal working hours from 1 February.
However, there can be exception by agreement or if something can't wait. Also, there can be staff on call, reports BBC.
A second principle is that workers shouldn't be disadvantaged by not answering the phone or picking up emails out of hours.
Public Administration Minister Petra De Sutter believes the change will boost efficiency.
She says the line between work and personal life has become increasingly blurred during the pandemic, with so many working from home.
Without the right to disconnect, she says, "the result will be stress and burnout and this is the real disease of today".
This rule change was relatively simple to put in place as it only applies to federal civil servants.
A plan to extend the practice to the private sector is expected to meet more resistance.
"The right to disconnect should not be expanded towards the private sector," says Eric Laureys from Voka, the Flemish Network of Enterprises.
He says it will "undo" progress seen during the pandemic towards more flexible working.
"It would be a major sign of distrust towards the ability of employers to organise work."
Len Shackleton, a research fellow at the Institute of Economic Affairs think tank and professor of economics at the University of Buckingham, agrees it undermines flexibility.
"Restrictions on contacting workers outside fixed hours is just a further dose of regulation."
Petra De Sutter insists the measure won't be a block on flexible working, when that is what employees want.
"But on the other hand, we need to protect basic rights of workers," she says.
Delphine laughs a little when I ask whether the change might feed into the notion of "clock-watching" civil servants.
She says it's an old cliché and that the workload has, over the years, increased.
"I think we do more with less people, usually. I don't think we are work-shy."
Other countries have brought in these kinds of provisions, most notably France.
In Belgium the next stage of the debate looks likely to be whether a greater proportion of workers should also gain the right to disconnect.