I have no idea. That's the problem with articles like these. they leave the impression that the company was just being evil...but no information on how the situation came to be.
During the stock market boom, many unions demanded that the pension funds be taken out of more secure traditional deposits and put into the market to an exceptional degree. This was combined with the liabilities being calculated based upon current growth and contributions cut to match - along with several other quirks.
This produced a kind of whipsaw effect.