Are Health Insurance Deductions from Payroll pre-tax or post-tax?

I've recently realized that my company was deducting too much from my check towards my health insurance. So now they have to reimburse me. Should my reimbursement check be tax-free since the amount deducted was from post-taxed income?
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Health insurance deductions don't have to be deducted pre-tax, but if your company has a Section 125 plan in place, they usually are. I know where I work, deductions are automatically taken pre-tax unless an employee specifies otherwise in writing, or there is a domestic partner covered. Therefore, if the deductions came out of your paycheck on a pre-tax basis, your reimbursement will be taxed. If the deductions came out on a post-tax basis, then your reimbursement would NOT be taxes as you have already had taxes withheld, and would not have to have any withheld again. Hope that makes sense.
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