The seventh edition of the "American Psychological Association Publication Manual" provides format and style guidelines for the behavioral and social sciences. The manual discusses a wide variety of references, but the U.S. Constitution is not covered. For legal matters such as this, APA style often relies upon "The Bluebook: A Uniform System of Citation," a writing guide for the legal profession.
When information from the First Amendment is included in the text, add a reference citation. The "Bluebook" style uses abbreviations and Roman numerals. After the material is presented, insert "U.S. Const. amend. I" without quotation marks inside parentheses; for example: (U.S. Const. amend. I).
If the First Amendment is cited in the text, put it on the reference page at the end. Because the citation's style is from the bluebook, its appearance is different from typical APA references. Use abbreviations and indicate "First" with a Roman numeral. The entry reads: U.S. Const. amend. I. Include the period after the Roman numeral.