---
kind: "section"
citation: "39 U.S.C. § 3631"
title: "39"
title_heading: "Postal Service"
number: "3631"
heading: "Applicability; definitions and updates"
release: "119-102"
date: "2026-07-12"
url: "https://uscodex.org/usc/39/3631"
units:
  - "Part IV — Mail Matter"
  - "Chapter 36 — Postal Rates, Classes, and Services"
  - "Subchapter II — Provisions Relating to Competitive Products"
---

# §3631. Applicability; definitions and updates

- (a) **Applicability.—** This subchapter shall apply with respect to—
  - (1) priority mail;
  - (2) expedited mail;
  - (3) bulk parcel post;
  - (4) bulk international mail; and
  - (5) mailgrams;

  subject to subsection (d) and any changes the Postal Regulatory Commission may make under section 3642.

- (b) **Definition.—** For purposes of this subchapter, the term “costs attributable”, as used with respect to a [product](/usc/39/102.md?p=6), means the direct and indirect postal costs attributable to such [product](/usc/39/102.md?p=6) through reliably identified causal relationships.
- (c) **Rule of Construction.—** Mail matter referred to in [subsection (a)](#a) shall, for purposes of this subchapter, be considered to have the meaning given to such mail matter under the mail classification schedule.

## Source credit

(Added Pub. L. 109–435, title II, § 202, Dec. 20, 2006, 120 Stat. 3205.)