It's more like trickle-up theory. If you have rules which make it more expensive to employ people over-and-above their wages and which restrict ability to use labour over-and-above work-time, then, without reducing wages or increasing work time, their labour can be applied more productively, increasing the product which then gets split between the more productive worker and the owner of the more productive capital.

Various shifts between pay and leisure can also become possible. A dynamic the mining union ran afoul of in the Kimberley mining industry when the workers revolted against a union attempt to stop a deal allowing the four-weeks-annual leave to be cashed out (since they were working on two-weeks on, two-weeks off basis anyway). So their work time went up by two weeks (to 26 weeks a year) but they got paid more.