Which specific actions trigger criminal prosecution under U.S. immigration law?

1. Entry and re‑entry: the most commonly prosecuted immigration crimes

Crossing the border without authorization (misdemeanor illegal entry) and returning after removal (felony unlawful re‑entry) are specifically criminalized in federal law—commonly prosecuted under 8 U.S.C. §§1325 and 1326—and have been the focus of mass prosecutions and programs such as Operation Streamline that dramatically increased case numbers since the mid‑2000s ^{[4] [1] [5]}.

2. Harboring, smuggling and aiding unauthorized presence

Federal statutes criminalize "harboring" or knowingly facilitating another person’s unauthorized presence and alien smuggling; 8 U.S.C. §1324 and related provisions authorize prosecutions of individuals who transport, shelter, or otherwise assist migrants, and prosecutors have used these statutes broadly, including against people who provide a range of assistance, which has prompted debate and spikes in indictments ^{[6] [7]}.

3. Fraud, false statements, and document‑related crimes that trigger criminal cases

Providing false information to immigration officials, using fraudulent documents, or making material misrepresentations can be charged as federal crimes—examples include prosecutions under federal false‑statement statutes cited in reporting—and these offenses can lead both to criminal penalties and severe immigration consequences like inadmissibility or visa revocation ^{[8] [9]}.

4. Criminal convictions that intersect with immigration outcomes (moral turpitude, aggravated felonies, etc.)

Separate from expressly "immigration" crimes are ordinary criminal convictions that immigration law treats as grounds for removal or bars to benefits: categories such as "crimes involving moral turpitude" and "aggravated felonies" are defined in the Immigration and Nationality Act and can make lawful permanent residents deportable, deny asylum or naturalization, or trigger bans on re‑entry—sometimes hinging on statutory definitions and judicial interpretation rather than label alone ^{[3] [10]}.

5. Enforcement reality: civil removal dominates, but policy drives criminalization

Although many immigration violations are civil and resolved in removal proceedings, Congress and executive policy decisions have steadily expanded the set of crimes that produce immigration consequences and have directed prosecutors to prioritize entry‑related and related criminal cases; data and advocacy groups show prosecutions escalated with programs like Operation Streamline and that prosecutorial discretion affects who is criminally charged ^{[1] [5] [11]}.

6. Who is targeted, disparities, and political context

Advocates and research groups document racial and geographic disparities in prosecutions—unauthorized re‑entry cases disproportionately involve migrants from Mexico and Central America—and multiple sources trace some statutes back to racialized policymaking in the 1920s, arguing that enforcement choices have reflected political priorities as much as public‑safety concerns ^{[4] [7]}.

7. Practical caveats: "conviction" definitions, plea consequences, and limits of reporting

Immigration law often uses an expansive definition of "conviction" that can include plea dispositions or forms of supervision that prosecutors and courts may treat as convictions for immigration purposes, which makes plea bargaining especially perilous for noncitizens; reporting underscores that criminal and immigration outcomes are intertwined but varies by jurisdiction and over time, and available sources do not resolve every statutory nuance or local prosecutorial practice ^{[12] [9] [3]}.

Conclusion: what actions specifically trigger criminal prosecution

In short, the specific actions that trigger criminal prosecution under federal immigration statutes include unauthorized entry and re‑entry (8 U.S.C. §§1325, 1326) and facilitating or smuggling/harboring migrants (e.g., §1324), while a separate class of ordinary criminal offenses—fraud, false statements, document crimes, and convictions classified as moral turpitude or aggravated felonies—can either be prosecuted criminally or converted into immigration removal consequences depending on charging decisions and statutory interpretation; policy choices and prosecutorial discretion largely determine whether conduct leads to criminal charges or civil removal ^{[4] [6] [8] [3] [1]}.