Nadine, I might be missing something here but aren't you entitled to 1 year unpaid mat leave by law in Australia????

I'm not sure what kind of work your half day job is in, but is there a HR policy or something that you can refer to?

I reckon your best bet is to talk to the manager and see if you can come to some kinda half way result. See why they want you fulltime and see if you can still achieve the same outcome but not working fulltime. Like, maybe you can negotiate that you could work full time during peak periods but part time 80% of the time... There are lots of permutations. I don't think your company would want to lose a valuable and experienced worker.

But really, I think looking for another role is a good idea - these folks don't sound accomodating!