As of 2011, the union membership rate for all workers in the US was 11.8%, which is down from 20% in 1983. That means just over one out of every ten workers today is unionized. Of these 14.8 million workers, almost 40% work in the public sector--in jobs in government, etc. that can't be outsourced. That means about 9 million workers in the *private sector* are unionized.
Thus, I find it incredible to argue that a few million Americans workers in a country of 300 million people are the reason why companies are outsourcing. In fact, more companies have outsourced since Reagan even though the unionization rate has nearly halved from 20% to 11.8%... so as Americans *leave* unions companies are also *leaving* our country.
Why? Because let's say you are Apple, and you want to make Iphones and PowerBooks, and you want to maximize profit which is your capitalistic right... so you have a choice. You can open a factory in China, where the workers make a dollar a day, don't ask for health care, don't ask for pensions, and work 16 hours a day without bitching for coffee breaks, or, you can open a factory in Texas, where even without unions the average Houstonian will want more than a dollar a day, some kind of health insurance, some kind of retirement plan, and no more than 8 hours a work a day.
Unions are only a small part of the picture. Outsourcing happens because our companies are exercising their right to pursue profit overseas, and have no obligation to hire workers who are more expensive just because they are fellow citizens. Until Americans stop b*tching and learn to compete with Asian workers then let the outsourcing continue--unless you want to pay $2000 for your next mobile phone, which is what it would cost if Samsung or Apple were to be forced to pay American wages to workers here.