Delta pilot's union in 2004 agreed to a 32.5% pay cut to help keep Delta out of bankruptcy. It didn't work. And in 2005 the Delta pilots also lost the pensions they had been promised in bankruptcy court. 2006 Delta asked for an additional 18% pay cut for pilots.

Unions are far from perfect. I've worked around union shops (Without being in a union) and know some of the insanity that comes with working with unions. BUT without a union an individual employee has very little power. Hired, fired, raises, no raises, good health care, crap health care, ... Individual employees get what the company decides to give. Unions successfully use the power of collective bargaining to balance corporate power against employee interests.

In Boeing's case, the machinists believe that Boeing reduced costs by killing employee pensions, shifting healthcare costs, and giving them terrible raises when times were good. Boeing showed that it didn't care about employees. It cared about further increasing profits. Now that times are bad for Boeing, they already soured the relationship with their union and the employees aren't interested in playing nice with the company that messed them over.