According to the IRS website:

The Taxpayer Advocate Service is Your Voice at the IRS!

The Taxpayer Advocate Service (TAS) is an independent organization within the IRS. We help taxpayers who are experiencing economic harm, such as not being able to provide necessities like housing, transportation, or food; taxpayers who are seeking help in resolving problems with the IRS; and those who believe an IRS system or procedure is not working as it should. Here are ten things every taxpayer should know about TAS:

1. The Taxpayer Advocate Service is your voice at the IRS.
2. Our service is free and tailored to meet your needs.
3. You may be eligible for our help if you have tried to resolve your tax problem through normal IRS channels and have gotten nowhere, or you believe an IRS procedure just isn’t working as it should.
4. The worst thing you can do is nothing at all!
5. We help taxpayers whose problems are causing financial difficulty or significant cost, including the cost of professional representation. This includes businesses as well as individuals.
6. If you qualify for our help, we’ll do everything we can to get your problem resolved. You will be assigned to one advocate who will be with you at every turn.
7, We have at least one local taxpayer advocate office in every state, the District of Columbia, and Puerto Rico. You can call your local advocate, whose number is in your phone book and in Pub. 1546, Taxpayer Advocate Service — Your Voice at the IRS. You can also call our toll-free number at 1-877-777-4778.
8. As a taxpayer, you have rights that the IRS must abide by in its dealings with you. Our tax toolkit at www.taxpayeradvocate.irs.gov can help you understand these rights.
9. TAS also handles large-scale or systemic problems that affect many taxpayers. If you know of one of these broad issues, please report it to us through our Systemic Advocacy Management System.

Source: IRS.gov Taxpayer Advocate