Some economists in Spain say that starting from this premise, and trying to apply it universally for the economy may have disastrous results.
The problem here is the effect on productivity. While there are some jobs where decreasing 20% of working hours while keeping productivity constant may be perfectly feasible, there are lots of jobs in Spain's precarious service-oriented economy where this is not possible.
For example, take all jobs depending on tourism: how is a waiter going to produce the same in four days of work than in five?
The same applies for Spain's public sector. Many public workers already have very good working conditions, but more importantly, the same effect described above also applies to them: it is not clear whether their working hours can be compressed without a significant loss of productivity.
To be clear I'm not against the idea, as there may be some merit to it if applied reasonably and on a tactical level, as part of much greater economic reforms. But I fear this is not what will happen; rather, populist politicians will take it and run with it because it sounds good, without any regards for its real implications, and without addressing the much harder and endemic problems of the Spanish economy such as the eye-watering unemployment levels and the lack of opportunities for our youth.