To be able to work with the IRS on behalf of a loved one:

The IRS requires a Form 2848 to be signed by your loved one, providing you the authorization to talk with the IRS. However, this might be too late.

To avoid this problem, have a Durable Power of Attorney prepared to have your loved one sign before they cannot make their own financial decisions. 

Durable Power of Attorney

The word “durable” means the authorization has staying power and will remain in effect if the principal becomes incompetent. The durable power of attorney must be created before your loved one becomes physically or mentally incompetent. Certain specific information required under the Internal Revenue Code and regulations must be included for a durable power of attorney to work for federal tax matters. 

By their nature, nearly all durable powers of attorney will not specify all of the required items for federal tax purposes – notably, a description of the matter (or matters) for which the representation is authorized, including the type of tax involved (such as income tax, gift tax, or civil penalties unrelated to an income or other tax return), tax form number, and specific tax year(s) or period(s) involved.

The durable power of attorney can still be used if the taxpayer’s appointed agent completes and signs Form 2848 on the taxpayer’s behalf, which contains the missing information.