The official employers guide to WARN states that people let go for cause are not counted under WARN.
The SpaceX position seems to be: 1) We just did our yearly performance reviews 2) Low performers were fired 3) Since they were all let go for cause, WARN does not apply.
Some people are claiming that it is a layoff and SpaceX is just trying to work around it. I'm imagining the SpaceX position here would be: 1) Layoffs are defined as letting employees go due to reduction in work or lack of money 2) SpaceX is experiencing neither of these 3) SpaceX plans to grow 20% this year; proof that there is no reduction in work 4) SpaceX has lots of open positions and is actively hiring; further proof that there is no reduction in work or lack of money
I have no knowledge of this lawsuit other then this article though.
Doesn't matter if they're layoffs for lack of work or performance-based firings: you still have to comply with the provisions of that law.
(I have no knowledge whether SpaceX did or did not comply, of course.)