Tesla filed 3 WARN notices in California in July so Musk or Musk’s lawyers at least know how to file them.
From what I understand, Twitter’s standard terms of severance allow for two months salary and benefits and some sort of accelerated vesting towards the next quarter. That’s been the big question for employees because they vest quarterly (though each person could have a different vest date) and the terms of the acquisition were that RSUs were converted to cash to be paid out on the vest schedule. Some in the press speculated that Musk was trying to avoid paying our November 1 vests by firing early, but given that you’d need a WARN notice anyway, that wouldn’t prevent anything. If there was an accelerated vest you missed by a few days, that might be something that could be avoided, but I don’t know.
Still, even if you are paying out two months of benefits and salary (and potentially maybe even more, with accelerated vesting), that doesn’t mean a company doesn’t have to file a WARN notice.
And with the expected figures being 25% of employees (~1800 people), that figure would qualify as a mass layoff by federal definition, irrespective of the company’s total size, and irrespective of the 50 or 100 per site thresholds that are true for specific states.
Or much more likely you give them 2-3 months severance which is basically the same as saying "you are laid off in 60 days, don't bother coming back to work". Technically they would be breaking the law but the severance would count against the damages under the WARN act so there's no reason to go to court about it.
EDIT: You might have to file with an elected official actually, the website is a bit unclear: https://edd.ca.gov/en/Jobs_and_Training/Layoff_Services_WARN
https://uscode.house.gov/view.xhtml?path=/prelim@title29/cha...
§2102. Notice required before plant closings and mass layoffs
(a) Notice to employees, State dislocated worker units, and local governments
An employer shall not order a plant closing or mass layoff until the end of a 60-day period after the employer serves written notice of such an order—
(1) to each representative of the affected employees as of the time of the notice or, if there is no such representative at that time, to each affected employee; and
(2) to the State or entity designated by the State to carry out rapid response activities under section 3174(a)(2)(A) of this title, and the chief elected official of the unit of local government within which such closing or layoff is to occur.
If there is more than one such unit, the unit of local government which the employer shall notify is the unit of local government to which the employer pays the highest taxes for the year preceding the year for which the determination is made.