The tax would technically be paid by the insurance provider or carrier. If there is more than one carrier, each carrier would pay the percentage of the excise tax commensurate with their percentage of the total premiums. And if a group is self-insured, then they would be responsible for their portion of the tax based on the self-insured premiums.
The details surrounding how the tax would be reported and paid are awaiting clarification and final regulations, but since the tax would be based on their employees’ total benefits packages, employers are currently responsible for calculating the tax and reporting each benefits administrator’s portion of the tax to the IRS. Employers, not benefits providers, may be penalized for incorrectly calculating the tax.