The idea here in France was just that, but it did not lead to more employment, one reason being that you work less for the same salary...paid for partly by the employer, with some contribution by the state.
It's effect on productivity is also unclear.
France already had one of the lowest volume of work per capita in OECD countries. Its generous and complex social benefit policies have some negative effects.
You can be permanently unemployed and receive up to 90% of minimum wage through a variety of social benefits.
But many of these benefits also apply if you earn a low salary, so your net income may actually decrease if you get a raise, because you may lose some benefits.
The labor market is very rigid. It is hard to fire employees.
Labor/management relations are very conflictual, and regulated. The shorter workweek was implemented across the board for all companies regardless of their size and industry, without much flexibility.