Compare to union shops though?

I know of some factories that shut down for annual maintenance for several months every year, and they lay everyone off. There is another factory (same company) that works opposite months of the year so in theory people are laid off and just switch between the two factories, but depending on schedule and work needs you can be out of work for a while.

I also know big projects often hire union labor (electricians, plumbers), and lay them off at the end of the project. I have no idea what the terms of this are.

You're comparing situations in different industries with different economics, never mind the union situations.

But that is the context if your read up a few levels we were told union shops have layoffs all the time. We cannot compare them is my point.