It's a stipulated requirement in most cases but enforcement of rules for employers is massively underfunded, so companies that don't have to deal with a union aren't bothered that much by regulations.

Government workers are well organized and don't notice that the rules they thought up (and are responsible for having enforced) actually are ignored by most non-government employers.

In fact, government is usually calling for a more flexible labor market, even though the Dutch labor market is among the most flexible in the EU (if not the most flexible as, again, any costs to getting rid of employees in an illegal fashion are neglible in the first place. They are also not enforced at all unless the illegally fired employee has the wherewithal to sue. Which is not trivial for lower paid people as access to subsidized legal help has been slashed. And even if you have a fixed term/hour contract, no country has as many temps and contractors which can be shown the door by the people paying their fees, which leads to unhealthy power dynamics with their immediate employer as well.)

So yes, in theory (and for government workers in practice) it's all nice.

It is only anecdotal evidence of course but I went for 24 hours a week back in 2019 and my employer (a ~unicorn scale-up in the Amsterdam region) was not fussed about it at all.

I'm a software dev and was one of the two employees with in-depth knowledge about a crucial part of the stack, so I had more leverage than most, but still the response was so much "yeah of course, we have to allow this by law" that I would be surprised if any of my colleagues would have had a different response.

I googled around a bit for legal cases and for advice aimed at Dutch companies, but because the law is so recent there's not much. My hunch (as someone who is perfectly clueless about legal matters) is that a restaurant or a shop might find it hard to argue that replacing one full-time worker with two part-time workers is impossible (given that the work is already organized into shifts) but perhaps companies that employ knowledge workers could successfully argue that you can't hire two part-time coders to do the work of one full-timer because the additional coordination costs in terms of additional meetings, additional equipment (i.e. laptop), perhaps the need for additional management personnel, and so on, are an unreasonable demand on the company. I could also see demands to reduce work to 4/5 be rejected when few people at work share your job description, because finding another employee willing to work 1/5 is really hard.

There's also the power dynamic to think of: are you really going to ask your boss to change your hours if you think that he/she will react badly and only grudgingly allow it?

Or maybe I'm completely off base... but anyhow, I guess I just wanted to point out that it's not clear to me whether this law has teeth.

> you can't hire two part-time coders to do the work of one full-timer because the additional coordination costs in terms of additional meetings, additional equipment (i.e. laptop),

"It would be more expensive" is clearly not an insurmountable problem. "But they don't have the requisite knowledge" is also not insurmountable, as it can obviously be mitigated by extra training.