The IRS has a number of Online Tools and Resources available from their website. Due to their high call volumes, you may want to explore those options first for faster service. If you determine you do need to call for assistance, the site instructs how to prepare for the call and the information you will want to have ready before you call.
IRS Hours of Telephone Service: unless otherwise noted (Alaska and Hawaii follow Pacific Time and Puerto Rico lines are open 8 a.m. to 8 p.m. local time).
Face-to-face assistance: In certain areas, the IRS has local offices you may visit to receive assistance. All offices operate by appointment.
The Telephone Assistance website provides information on numbers available for IRS assistance for individuals, businesses, exempt organizations, retirement plan administrators, government entities, people with hearing impairments, individuals who believe they may be a victim of identity theft, people who live outside the United States and a list of local IRS offices.
The Telephone Assistance Contacts for Business Customers website provides more specific information on phone assistance for business customers, electronic filing, and tax-exempt and government entities.
The Telephone Numbers for FBAR and Title 31 Help website provides a number for technical Title 31 (Anti-Money Laundering) and FBAR (Report of Foreign Bank and Financial Accounts) questions.
The U.S. Citizens and Resident Aliens Abroad website provides contact information including a TOLL number (not toll-free) to the IRS Philadelphia office which provides international assistance. It also contains information on permanent IRS offices outside the United States.
The IRS website Practitioner Priority Service provides phone support for tax practitioners who have account-related questions with valid third-party authorizations (i.e. Forms 2848 Power of Attorney and Declaration of Representative, 8821 Tax Information Authorization, and/or 8655 Reporting Agent Authorization).
Note that any link in the information above is updated each year automatically and will take you to the most recent version of the webpage or document at the time it is accessed.