Again, I'd have to dispute that - they were hired for a job, knowing full-well that they were going to receive straight salary and benefits, but were not eligible to get paid overtime. That's exactly the basis under which I was hired (and I accepted those terms of employment just as they did - nobody held a gun to my head).
So, one or more of those employees got greedy and decided after the fact that they didn't like the terms of the agreement under which they were employed (that they had previously agreed to). (Or, more likely, they were spurred on by greedy union goons salivating over the thought of organizing thousands of highly-paid technology employees (and their union dues, and the power that it would bring to those few at the top of the union), not out of concern for the workers, but rather, as with most union organizing efforts, out of the not-so-enlightened self-interest of the union organizers themselves, the union bosses, et al.)
They got some lawyers and a court to change things, hoping or expecting that they'd reap some extra compensation above and beyond that which they had agreed upon, while mistakenly thinking that IBM would simply end up giving everybody more $$ for the same amount of work that they were already doing. Instead, they ended up messing around with everybody else's livelihood and work life. Just one more example of "killing the golden goose".