Hourly wages versus salary & commission-based pay

Does anyone know of any laws or regulations that directly or indirectly encourage hourly wages versus salary and commission-based pay?

One example I can think of is union laws that, basically, give unions the power to demand and receive hourly wages for their members. However, this is a really broad and not very detailed example. Can anyone think of better examples?

I would also really love to see this. Sorry to not contribute anything… but bump.