The Union may be weaker than in 1997, but UPS is not in the position they were either, in 1997. A strike would be far worse for UPS now...
-In 1997 UPS did not had not gone public with their stock yet. Can you imagine what a strike would do to the stock price both short and long term? UPS was able to set the stock price back then. I imagine a looming strike today would send the stock down 30%, and an actual strike perhaps 50%+. The stock would not recover for at least a year, unless the Union was completely illiminated.
-In 1997 our competitors were far less equipped to handle our volume. RPS/Fed-Ex ground had barley achieved nation-wide coverage, and if I remember correctly RPS was not even delivering residentials (or perhaps a few). Fed-Ex today would poach all the best customers by offering the full array of services nationwide without the threat of a strike...ever. Imagine how Amazon would react. We would lose customers permanently since Fed-Ex can now do it all.
-In 1997 the unemployment rate was lower. Plus I believe the workforce has become less enthusiastic about long hours. Part timers would not cross, they would simply get a job at Amazon or somewhere else, for the same, or better money.
I imagine the cost of a strike to UPS would have to be measured in billions (or tens of billions) rather than hundreds of millions, this time around.
Both sides lose big in a strike. Even bigger given today's circumstances.