The tax power of attorney form allows a person to file taxes on your individual and business behalf with the State. The document is only valid for that year of filing and it is recommended that the principal choose someone that is a professional such as an accountant or attorney as any wrongdoing reflects back on the principal, not the person assigned.
The document does not need to be notarized but signed by the principal and person authorized to carry out the tax filings.

Source: http://www.revenue.alabama.gov/salestax/2848a.pdf