It can be a bit more complicated than that Pamelat- nursing strikes/breast refusals are difficult problems that need some expert intervention. If you want to move to formula, that's up to you but the baby is not necessarily 'choosing' it as such.
Often - IME and following lots of reading, but please speak to someone as I'm not a BF counsellor - refusals are sometimes because a baby cannot suck... perhaps because of illness, pain or exhaustion/hunger. It is important to rule these out I think, with the help of a professional/BFC. Certainly the first nursing strike we had was because of illness.
It can then however slip into a more 'emotional' vicious circle though, with me it was trying the breast even though he rejected it. I wish then I'd been more laid back and followed the advice of BF counsellors about making sure he had enough milk even if formula, and allowing him to come back to the breast on his own terms with lots of skin contact, snuggling, co-sleeping and less routine and stress.
If I had done this, I think I probably wouldn't have experienced a later, longer and worse nursing strike also.
If you want more info on this please ask me, or look at the La Leche League site or ring them or visit the www.kellymom.com
My little one was older though, and could virtually self latch with the first strike and definitely with the second; I'm not sure how I would have coped with a 6 week old.