It is true that the Constitution does not give foreigners the right to enter the U.S. But once here, it protects them from discrimination based on race and national origin and from arbitrary treatment by the government. Immigrants work and pay taxes; legal immigrants are subject to the military draft. Many immigrants have lived in this country for decades, married U.S. citizens, and raised their U.S.-citizen children. Laws that punish them violate their fundamental right to fair and equal treatment.
—from the "Immigrants' Rights" section of aclu.org