A big thing a union could shoot for is fixing the mechanical rights in advertising. No more one-time payments, but the option of royalties. SA is far behind the world on this and a lot of composers have been screwed
I've heard a horror story about a musician working for a big BBC production, that got ignored once all the work was done...ignored as in not paid, or credited. I don't know if it's worse here than it is overseas, but it would be horrible if we get a reputation as a country where "the musicians work for free".