IRS Code: Levy of Federal Payments

The IRS may garnish your Social Security benefits UP TO 15% or 100%, but nothing in between. There are some exceptions that apply, however, as a general rule, the IRS may not take more than 15% of your federal payment. If you are experiencing a Social Security or wage levy in excess of 15%, contact the Patriot Network for assistance.

§6331 (h)

(h) Continuing levy on certain payments
(1) In general
If the Secretary approves a levy under this subsection, the effect of such levy on specified payments to or received by a taxpayer shall be continuous from the date such levy is first made until such levy is released. Notwithstanding section 6334, such continuous levy shall attach to up to 15 percent of any specified payment due to the taxpayer.
(2) Specified payment
For the purposes of paragraph (1), the term “specified payment” means—
(A) any Federal payment other than a payment for which eligibility is based on the income or assets (or both) of a payee,
(B) any payment described in paragraph (4), (7), (9), or (11) of section 6334 (a), and
(C) any annuity or pension payment under the Railroad Retirement Act or benefit under the Railroad Unemployment Insurance Act.
(3) Increase in levy for certain payments
Paragraph (1) shall be applied by substituting “100 percent” for “15 percent” in the case of any specified payment due to a vendor of goods or services sold or leased to the Federal Government.

The 100% occurs under the Jeopardy assessment rule.

§6331 (i)

(i) No levy during pendency of proceedings for refund of divisible tax
(3) Exceptions
(A) Certain unpaid taxes
This subsection shall not apply with respect to any unpaid tax if—
(i) the taxpayer files a written notice with the Secretary which waives the restriction imposed by this subsection on levy with respect to such tax; or
(ii) the Secretary finds that the collection of such tax is in jeopardy.
(B) Certain levies
This subsection shall not apply to—
(i) any levy to carry out an offset under section 6402; and
(ii) any levy which was first made before the date that the applicable proceeding under this subsection commenced.

Source: http://www.law.cornell.edu/uscode/html/uscode26/usc_sec_26_00006331----000-.html