Can I take a Dead Sea Salt bath whilst breastfeeding?

It's considered safe.  Anecdotally though, I will say that we have a high number of patients who suffer a severe drop in milk supply after a salt bath.  There's no medical confirmation and no logical reason for it, but it seems to happen. 

You can, it’s safe. They have to put that on there so that people can’t sue them should something go wrong it is not their fault

you should probably be seeing your healthcare provider then

It's fine. Companies usually put that warning on labels *not* because there is any known harm to a fetus or baby, but because they don't want to spend the research dollars to prove that fact, yet still want to cover their a**es legally in cause some moron decides to sue. Taking a mineral or epsom salt bath is completely safe during both pregnancy and breastfeeding, though you may want to run it by your GF or OP if you want to take epsom salts as a laxative.