As I found out recently, not all EU countries have minimum wage regulations but free work is not allowed unless it is part of an internship agreement, as a volunteer for a NPO or similar, which is not the case for P2F, simply because they pay to do work. Basically it is illegal.
In most countries, all of these still need to cover the volunteers for "on the job" accidents.
To pay to work has been unheard of until now. Slavery has a "work against one' s will" factor, P2F is a voluntary sacrifice.
The idea is that it' s a crime if someone kills you but it' s not if you kill yourself.
If they can clear insurance and liability hurdles through paperwork, they can not clear ethical, moral and labour law issues.