A lot of the discussion here is about statutory rights (under the Civil Rights Act), not constitutional rights. But, if we just talk about the latter: under US

A lot of the discussion here is about statutory rights (under the Civil Rights Act), not constitutional rights. But, if we just talk about the latter: under US constitutional law, national origin is a "suspect class" which demands "strict scrutiny" under the equal protection clause of the 14th Amendment (as developed by the Supreme Court's case law). The other "suspect classes" are race, religion and "alienage" (the state of being a non-US citizen). There are also two "quasi-suspect classes", discrimination on the grounds of which is subject to the weaker "intermediate scrutiny" – sex/gender (which possibly includes sexual orientation/gender identity) and legitimacy of birth. All other discriminatory grounds (age, disability, wealth, politics, criminal record, etc) are only subject to the weakest "rational basis review". But "strict scrutiny" is not an absolute bar on discrimination, it just means the government has the onus of convincing the Supreme Court that the discrimination is necessary to obtain a "compelling state interest". Even though US immigration law obviously discriminates against non-US people on the basis of national origin and "alienage", the US government has never had any trouble convincing the Supreme Court that immigration law serves a "compelling state interest". That's a point a lot of people don't get about discrimination law (whether statutory or constitutional) – discrimination per se is not illegal, even on protected grounds. Rather, discrimination is illegal when it lacks a sufficiently compelling justification, with the strength of justification required depending on how strongly protected those grounds are.