Yes, by Congress, even if and when required by a treaty or other international agreement. Look up §101(a)(15) of the Immigration and Nationality Act, codified a

Yes, by Congress, even if and when required by a treaty or other international agreement. Look up §101(a)(15) of the Immigration and Nationality Act, codified at 8 USC §1101(a)(15), for all the nonimmigrant classifications: https://www.law.cornell.edu/uscode/text/8/1101 https://www.law.cornell.edu/uscode/text/8/1101 8 USC §1101(a)(15)(H)(i)(b) has H-1B, 8 USC §1101(a)(15)(E)(iii) has E-3, and so on. A treaty is not self-executing under US law unless it is both ratified by 2/3 of the Senate pursuant to the Treaty Clause of the Constitution and also contains language expressing that it will be self-executing upon ratification, in which case it has the same domestic legal effect as an Act of Congress. See Medellín v. Texas, 552 U.S. 491 (2008), https://en.wikipedia.org/wiki/Medell%C3%ADn_v._Texas https://en.wikipedia.org/wiki/Medell%C3%ADn_v._Texas for a recent SCOTUS precedent about this. Many agreements which are treated internationally as treaties, including most US free trade agreements, are not considered as such for purposes of US constitutional law; many others are not self-executing even when they are ratified through the Treaty Clause procedure. These only have effect in US domestic law when implemented by implementing legislation passed by Congress, or to whatever extent the executive branch handles implementation through regulations, policies, or similar which it already has the authority to promulgate without new legislation.