The other day, I got to thinking about why the Department of Homeland Security could unilaterally change immigration laws so that people who were legally in the country one day were classified as illegal immigrants the next. To me that seemed so at odds with the ex post facto clause in the Constitution.

The answer to that question is a bit frightening.

While the Constitution prohibits specifically retroactive laws (Article I, Section 9, Clause 3), this prohibition applies only to criminal cases, not civil matters, and immigration is considered a civil matter, even when the government is using criminal justice mechanisms, such as incarceration facilities and police powers, or carrying out actions like deportation or visa revocation.

Despite the fact that immigration is considered a civil matter, illegal immigration is made a federal crime in the United States, primarily through 8 U.S.C. § 1325 (Improper Entry by Alien) and 8 U.S.C. § 1326 (Reentry of Removed Aliens)

The classification of immigration as a civil matter is not addressed in the Constitution, but was established by in Fong Yue Ting v. United States, 149 U.S. 698 (1893). This ruling also determined that deportation is not “punishment” in the legal sense, but rather the government’s refusal to allow someone to remain, and because they are not considered “punishments,” Congress or the Executive Branch can retroactively apply new immigration grounds for exclusion, even if those grounds did not exist when the non-citizen entered the country. In addition, statutes, such as those that make past criminal activity grounds for deportation (e.g., membership in certain organizations or criminal behavior), can be applied to actions taken before the law was passed.

So, if every major law dealing with unauthorized immigration is a criminal statute, how can immigration enforcement be a merely civil matter?

As a side note, while subsequent Supreme Court decisions have maintained the legal fiction established by the Fong Yue Ting precedent, I can’t find any legal reason why Congress couldn’t pass a law declaring that any immigration proceedings should be considered as criminal matters, given that the government is already treating them that way, except without many of the procedural safeguards required Constitutionally in criminal proceedings involving U.S. citizens.