Yes, employers employ labor to get work done...but "work" is essentially product, and that is for whom, eh???? Ultimately, the consumer, who is overwhelmingly LABOR. So while each idiot employers views everything from his own little prism, in fact, if the balance between producer and consumer (labor) is broken, the producer (employer) goes down just as surely.
Quite obviously, the employer and consumer balance right now is totally out of whack, among other things, due to intrinsic processes, but mostly due to the INSANITY of the current Republican power structure.
But I think that shortening the working day right now would increase the labor supply, when the problem is that globally there is a massive surplus of labor, and you cannot impose tariffs because any increase of trade barriers would likely result in world war. Increasing the labor supply would depress wages, which is the last thing needed...in fact, raising wages would help this economic recession a great deal.
As for who would enforce any G7 (it would have to be G20, not just the G7) agreement, so far treaties are fairly effective, unless imposed by force, and threat, like Versaille.