I'm with UPS here.. the Employees were not in a position to strike, so they performed an illegal strike under the Union's agreement with UPS. They are well within their rights to fire them all on the spot.
You can't just decide not to do your job for 90 min without giving prior notice and expect to still have your job.
Second, why do UPS and other groups like that get a discount on their parking tickets ? Well for one they collect SO many. Most delivery services inside cities get these kinds of breaks, because they CAN'T do their job without getting the tickets, and they get them in such numbers that not giving them a discount would either force the businesses out, or make for large rates spikes. It's not just UPS, Fedex, USPS, but also groups like Coca Cola and Pepsi delivery trucks, etc.
Normally when Cities pull that card, what happens is the delivery co's start by just not delivering to the City Gov't. Sorry, couldn't find a parking spot. Come pick up your package/pallet/etc at this address within X days.. Which is something the CITY can't afford to do, and it just blows up in their face.
End of the day, the Employees didn't think about what they were doing, and now they are gonna deal with it. The City made a threat, and UPS called them on it. City should mind it's own business and not make threats over employees being LEGALLY dismissed. This isn't some shady grey area, it's black and white. It's why the Union isn't going to war, cause they know it too.