(c) The Act's prohibition against interference prohibits an employer from discriminating or retaliating against an employee or prospective employee for having exercised or attempted to exercise FMLA rights. For example, if an employee on leave without pay would otherwise be entitled to full benefits (other than health benefits), the same benefits would be required to be provided to an employee on unpaid FMLA leave. By the same token, employers cannot use the taking of FMLA leave as a negative factor in employment actions, such as hiring, promotions or disciplinary actions; nor can FMLA leave be counted under no fault attendance policies. See § 825.215.
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I'll also point to things like Employer Makes $1.3 Million FMLA Mistake by Firing Worker After Mexico Trip that demonstrate the "be careful when dealing with discipline of people who are on FMLA and check with a lawyer first." https://www.shrm.org/resourcesandtools/legal-and-compliance/...
If they are on FMLA you can’t fire them but you can eliminate their job. However, if they are on a leave unrelated to FMLA there might be no protections and the employee can be terminated.
And during the holidays at end of year, when hiring seems to slow down for a couple months.