U.S. Code Title 8 - In-state Tuition for Illegal Aliens
U.S. Code Title 8, Chapter 14, Subchapter II, § 1623 addresses preferential treatment of illegal aliens in higher education.
8 USC § 1623 - Limitation on eligibility for preferential treatment of aliens not lawfully present on basis of residence for higher education benefits
(a) In general
Notwithstanding any other provision of law, an alien who is not lawfully present in the United States shall not be eligible on the basis of residence within a State (or a political subdivision) for any postsecondary education benefit unless a citizen or national of the United States is eligible for such a benefit (in no less an amount, duration, and scope) without regard to whether the citizen or national is such a resident.
(b) Effective date
This section shall apply to benefits provided on or after July 1, 1998.
Source: Cornell Law School Legal Information Institute: 8 USC § 1623