There is absolutely no reason a worker in Bangladesh, for instance, should be paid less than a worker in Silicon Valley, for the same work.
Well, actually there is...
Employing someone in e.g. Bangaldesh is cheaper for a couple of reasons:
1) lower overheads such as employment safety, welfare, working hours, etc.
2) lower cost of living for those employees because of lack of building safety standards, food safety standards, etc. and the fact that it is a por country without the resources to raise people out of poverty.
Now, the astute amongst you will realise these are buisness reasons, not moral ones. If you follow them, then the natural pressure will be to either reduce standards in the countries that are losing jobs, or raise them in the ones gaining jobs. Over time, the second of these is more likley to happen, due to the natural flow of capital into poorer countries, but in the shorter term, in the name of "business", certain individuals would like to implement the first in the name of increased profit. They'll do so by preventing unionisation, and extolling the virtues of "competitiveness" amongst other things.
Corporations, as non-human entities, have no morals, which is why legislation has to provide them for them. minimum standards, minimum pay, helath and safety, et al.