In the United States, employers with more than 100 full-time, non-probationary employees must provide 60 days notice of most planned layoffs[0]
> - LIFO principle for layoffs, newest employees are let go first. Stack ranking not possible
This is functionally equivalent to a stack ranking in that it is a forced-distribution scheme. It is just based on a single factor that is outside of the employee's control. Say what you want about stack ranking, but people do have a large degree of control over their job performance.
> Any kind of discrimination is forbidden
In the United States any kind of job discrimination against members of protected classes[1] in illegal. Even inadvertently disparately impacting[2] members of a protected group is illegal.
0 - https://www.dol.gov/general/topic/termination/plantclosings
1 - https://www.eeoc.gov/employers/small-business/3-who-protecte...