On April 19, the United States Citizenship and Immigration Services (USCIS) issued a policy guidance, clarifying that violations of federal controlled substance law are generally a bar to establishing good moral character for naturalization, even where that conduct would not be an offense under state law. The requirement of good moral character has been a requirement for naturalization since March 26, 1790, when Congress passed the Naturalization Act of 1790.

According to the USCIS Policy Manual, an applicant involved in certain marijuana-related activities, such as possession, manufacturing, production, distribution, or dispensing, even if legal under state law, could be found to lack good moral character. Likewise, an applicant's receipt of a financial benefit from a spouse or parent's trafficking may preclude a finding of good moral character. These activities could be established by a conviction or an admission by the applicant. The conditional bar to good moral character for a controlled substance violation does not apply if the violation was "a single offense for simple possession of 30 grams or less of marijuana."

The Controlled Substances Act classifies marijuana as a Schedule I substance and prohibits its possession (unless it is a single offense of simple possession of 30 grams or less) even if it for medical use. Some states permit the home cultivation of marijuana or the possession of much more than 30 grams of cannabis. However, USCIS has been denying U.S. citizenship to individuals admitting to be employed in the marijuana industry legalized in some states. USCIS policy on this issue might be subject to legal challenge. Naturalization denials can be appealed within the agency and then to federal court.