All tests are optional. However most hospitals in Australia recommend having a GBS swab, despite the infection being transient so a +ive result does not mean you will be +ive in labour. Ditto a -ive result is no guarantee your child will not be affected.
:yeahthat: They can't make you do anything you don't want to do. Unfortunately I think many health care providers use language that suggests that it's not optional.

I know the infection is transient and ditto what Traveller said, but I *think* the risks to baby if you are GBS positive, whilst low, can be quite deadly. I might be confused on this though - I'm sure there's heaps of accurate information available if you research it.