Power of Congress and the Executive to Exclude Aliens: Constitutional Principles [December 30, 2019] [open pdf - 2MB]
From the Document: "Under long-standing Supreme Court precedent, Congress has 'plenary power' to regulate immigration. This power, according to the Court, is the most complete that Congress possesses. It allows Congress to make laws concerning non-U.S. nationals (aliens) that would be unconstitutional if applied to citizens. And while the immigration power has proven less than absolute when directed at aliens already physically present within the United States, the Supreme Court has interpreted the power to apply with most force to the admission and exclusion of nonresident aliens. The Court has upheld or shown approval of laws excluding aliens on the basis of ethnicity, gender and legitimacy, and political belief. It has also upheld an executive exclusion policy that was premised on a broad statutory delegation of authority, even though some evidence considered by the Court tended to show that religious hostility may have prompted the policy. Outside of the immigration context, in contrast, laws and policies that discriminate on such bases are almost always struck down as unconstitutional. To date, the only judicially recognized limit on Congress's power to exclude aliens concerns lawful permanent residents (LPRs): they, unlike nonresident aliens, generally cannot be denied entry without a fair hearing as to their admissibility."
CRS Report for Congress, R46142
Congressional Research Service: https://crsreports.congress.gov/