The FMLA states that "Upon return from FMLA leave, most employees must be restored to their original or equivalent positions with equivalent pay, benefits, and other employment terms. Use of FMLA leave cannot result in the loss of any employment benefit that accrued prior to the start of an employee’s leave."
One way your company would be able to reduce your vacation days is if you took days off in addition to the days you able to take off under the FMLA. There may also be a company policy regarding vacation days and how it is affected by the FMLA that I would want to see before being able to give you a firm answer to your question. The FMLA allows employers to require employees to use up paid leave first, so paid and unpaid leave run concurrently.
The key part I will need to determine is if you were paid for the 8 vacation days that your employer used while you took medical leave. The answer to your question depends on whether you were paid for the vacation time that was used.
If you do in fact have a case, an attorney would be able to help you by drafting a demand letter stating that you are entitled to receive full benefits upon returning from the FMLA. If they do not restore your vacation time benefits, a complaint can be filed against with the Department of Labor.
If you have any further questions, please feel free to contact me.
It is not clear to me from your question whether, upon your return from leave, your employer deprived you of vacation days you had accrued PRIOR to commencement of your FMLA leave or vacation time you believe accrued DURING that leave. Each presents a different scenario and implicates different rules and regulations. Without knowing the specific facts, let me give you a couple of very general guidelines.
If The Vacation Days You Are Referring To Accrued Prior To The Commencement Of Your FMLA Leave:
An employer is entitled to "require … [you] to substitute accrued paid leave for unpaid FMLA leave," see 29 CFR 825.207(a), but it is supposed to notify you beforehand that it is going to require such substitution. If it didn't properly notify you it was going to require paid and unpaid FMLA leave to run concurrently, you may have a legitimate basis for demanding that it reinstate the now-eliminated vacation days. 29 CFR 825.207(b). After all, it is not entitled to retaliate against you for having taken FMLA leave.
If The Vacation Days You Are Referring To Accrued During The Course Of Your FMLA Leave:
An employer is required to "maintain … [an] employee's coverage under any group health plan … on the same conditions as coverage would have been provided if the employee had been continuously employed during the entire leave period." HOWEVER, "[a]n employee's entitlement to benefits OTHER THAN group health benefits during a period of FMLA leave (e.g., holiday pay) is to be determined by the employer's established policy for providing such benefits when the employee is on other forms of leave (paid or unpaid, as appropriate)." 29 CFR 825.209(h). You should consult an employment lawyer in your state to go over the amount of your FMLA leave that was paid and the amount unpaid, what your employer's policies provide regarding the accrual of benefits during paid and unpaid leave, and what it has done in this instance.
Without more information, it is simply impossible to know how any of these or, indeed, other rules and regulations apply to your situation. Good luck.
Disclaimer: This answer does not establish an attorney-client relationship or constitute legal advice. It is for general informational purposes only.