Unfortunately, in an economic environment like this a union won't help you. We're seeing many public services staff that are unionized laid off (in Canada) and I'm sure this is happening around the world. By the end of this it's quite likely this will look similar to the Great Depression.
It wouldn't stop all the layoffs but that isn't the goal. The goal would be to give employees a vote when decisions are made on how to deal with the economic fallout instead of being the passive victims of whatever decision is arrived upon by upper management and the board.
Instead of instantly laying off as many people as possible, the union could have brought other proposals to the table to try and help both the company and employees. Maybe you delay 401k matching until the end of the year instead of paying it every paycheck. Maybe cut employee salaries and hours instead. The union at least gives the employees the chance to voice ideas on how to help the company and themselves make it through instead of finding out that 400+ of your coworkers were let go over Zoom via a two minute prerecorded message.
Let's assume that's true (it's not always true, but let's assume it is): isn't this still better than sorting by "only execs get taken care of and everyone else gets screwed by default"? I'd rather have someone voicing my concerns even if the person who's been there longer gets taken care of more.
A union could have helped negotiated the amount the lowest paid among us was cut vs the amount execs were cut, for example. I don't know the details of this specific case, so I don't know if there was another viable option, but at least if we had a group of the workers who did know I would have some confidence that there really was no other way and this wasn't just management cutting everyone elses pay to avoid having to lose a couple million themselves.