If an appropriation bill is enacted that increases spending within a fiscal year, such as in a supplemental spending bill, but after the regular sequestration time has passed, two things may happen: Either a “within-session sequestration” or a look-back adjustment occurs. A within-session sequestration is an order for an across-the-board reduction in discretionary spending ordered within 15 days of the offending bill’s enactment, if it is so enacted before July 1 of the fiscal year. A “sequestration“ or cancellation of discretionary budget authority, normally is ordered for a fiscal year pursuant to a Final Sequestration Report, within 15 days of the end of a session of Congress. The “look-back” procedure occurs if the bill or joint resolution causing the breach is enacted on July 1 or after, but instead of a sequestration order, the subsequent fiscal year’s spending limit is adjusted downward by the amount of the breach.
Section 251(a)(6) reads as follows:
“(5) Look-back.—If, after June 30, an appropriation for the fiscal year in progress is enacted that causes a breach within a category for that year (after taking into account any sequestration of amounts within that category), the discretionary spending limits for that category for the next fiscal year shall be reduced by the amount or amounts of that breach.
(6) Within-session sequestration.—If an appropriation for a fiscal year in progress is enacted (after Congress adjourns to end the session for that budget year and before July 1 of that fiscal year) that causes a breach within a category for that year (after taking into account any prior sequestration of amounts within that category), 15 days later there shall be a sequestration to eliminate that breach within that category following the procedures set forth in paragraphs (2) through (4).
BEA Joint Explanatory Statement
The joint explanatory statement for the Conference Report on the Budget Enforcement Act of 1990 describes a within-session sequestration by the below text (italics added):
During the session in which the fiscal year begins, the enactment of legislation causing a breach in the spending limits of any category would trigger a presidential sequestration order that would impose across-the-board cuts in that category bringing spending down to the established limits. This presidential sequestration order would be issued within 15 days after the end of a session of Congress. During the following session, the enactment of legislation causing a breach in the spending limits would trigger sequestration 15 days after enactment if the legislation were enacted before July 1, or would reduce the applicable spending limits for the next fiscal year by the amount of the breach if the legislation were enacted on or after July 1.
U.S. Congress, Budget Enforcement Act of 1990: Conference Report for H.R. 5835 (H. Rept. 101-964) November 5, 1990.