Answered By: Jason Puckett Last Updated: Aug 16, 2016 Views: 5336
According to the 7th edition of the MLA Handbook (p.205), "In general, do not italicize or enclose in quotation marks the titles of laws, acts, and similar documents in either the text or the list of works cited (Declaration of Independence, Constitution of the United States, Taft-Hartley Act). Such titles are usually abbreviated, and the works are cited by sections. The years are added if relevant."
Also, Purdue University's Online Writing Lab (Purdue OWL) has an example of how it may look in MLA format. It is in the OWL FAQS and under the section "How do I cite the US Constitution in MLA?" toward the bottom of the page.