Was that in EU? At least in Germany if those employees work on the same thing/branch/team, this would be quite difficult (from a legal perspective) for the employer to do.
In the US we have what's called at-will employment in 49 of 50 states. It means that (barring protected reasons like age/race/gender/family status) employers can terminate their employees at any time with no notice, for any reason or no reason.
"The protection goes both ways" they say, as you can leave your job and quit with no notice just the same, but it's quite an imbalance as the employee leaving does not generally have any impact on the employer's health insurance, while employees generally do depend on their employer-provided health insurance.
"The protection goes both ways" they say, as you can leave your job and quit with no notice just the same, but it's quite an imbalance as the employee leaving does not generally have any impact on the employer's health insurance, while employees generally do depend on their employer-provided health insurance.