The Centralized Authorization File (CAF) number is a 9-digit number assigned to individuals based on the filing of Form 2848, Power of Attorney and Declaration of Representative.
Per IRS Instructions for Form 2848 Power of Attorney and Declaration of Representative, on page 4:
Enter the full name and mailing address of your representative(s). You may only name individuals who are eligible to practice before the IRS as representatives. Use the identical full name on all submissions and correspondence. If you want to name more than four representatives, write “See attached for additional representatives” in the space to the right of line 2 and attach an additional Form(s) 2848.
If you want to authorize your representative to receive copies of all notices and communications sent to you by the IRS, you must check the box provided under the representative's name and address. You may not designate more than two representatives on Form 2848 (or designees on a Form 8821) to receive copies of notices and communications sent to you by the IRS for the same matter(s). Do not check the box if you do not want copies of notices and communications sent to your representative(s).
Note. Representatives will not receive forms, publications, and other related materials with the correspondence.
Enter the nine-digit CAF number for each representative. If the IRS has not assigned a CAF number to the representative, enter “None,” and the IRS will issue one directly to the representative. The CAF number is a unique nine-digit identification number (not the SSN, EIN, PTIN, or enrollment card number) that the IRS assigns to representatives. The CAF number is not an indication of authority to practice. The representative should use the assigned CAF number on all future powers of attorney. The IRS will not assign CAF numbers for employee plan status determinations or exempt organization application requests.
If your representative cannot remember his or her CAF number, they may contact the Practitioner Priority Service (PPS) at 866-860-4259. PPS will assist your representative in retrieving the assigned CAF number.
Enter the PTIN, if applicable, for each representative. If the IRS has not assigned a PTIN, but the representative has applied for one, write “applied for” on the line. Unenrolled return preparers must possess a valid PTIN to represent a taxpayer before the IRS.
Check the appropriate box to indicate if the representative's address, telephone number, or fax number is new since the IRS issued the CAF number.
The post-employment restrictions in 18 U.S.C. 207 and Circular 230, section 10.25, apply to a representative who is a former employee of the federal government. The Treasury Inspector General for Tax Administration may enforce criminal penalties for violations of the restrictions, and the Office of Professional Responsibility may take disciplinary action against the practitioner.
Qualifying students or law graduates in LITCs and STCPs. You must list the lead attorney or CPA as a representative. List the lead attorney or CPA first on line 2, then the student on the next line. Also see Part II. Declaration of Representative, later.
Note that any link in the information above is updated each year automatically and will take you to the most recent version of the document at the time it is accessed.