The 14th Amendment to the U.S. Constitution mandates that all people born on U.S. soil and subject to the jurisdiction of the U.S. are citizens. Legally, this is known as jus soli, the latter word from "soil". This contrasts with jus sanguinis, where a child acquires a country's citizenship by right of one or more parents being a citizen of that country. To my knowledge, most countries observe a combination of jus soli and jus sanguinis. The U.S. does both. Some countries will grant citizenship to children of aliens born on their soil only if one parent is a citizen or permanent resident; France, Singapore and Germany are some examples.
A bill by Representative Nathan Deal, a Republican from Georgia, reported by the Atlanta Journal-Constitution, would seek to modify jus soli in the U.S. Opponents of "birthright citizenship" says it encourages illegal immigration, because undocumented immigrants can get U.S. citizenship for their children born in the U.S. The anti-immigrant crowd also says this encourages chain migration, whereby a citizen child can sponsor their parents and eventually their parents' relatives. In practice, U.S. citizen children have to wait till age 21 to sponsor non-citizen parents. There are significant waiting lists for non-nuclear relatives.
At present, it would absolutely be unjust to modify jus soli even if it were constitutional. It would cut a lot of people - children, mind you - off from public benefits. That said, changing jus soli can be justified in certain cases. People migrate far more than when the Constitution was written. Countries do have the right to exercise reasonable control who they admit so that their public services are not overburdened. Mr. Deal's law is unlikely to pass Congress or to survive a legal challenge, and this is as it should be. However, if jus soli were modified, there are other legal changes that the U.S. would need to make:
1. All children have the right to an education under Article 26 of the Universal Declaration of Human Rights. All children in the U.S., regardless of the immigration status of their parents, should be educated and treated as equals in U.S. schools; in fact, in Plyler v. Doe, the courts have rejected legal challenges to the right of undocumented children to education.
2. Children, regardless of immigration status, ought to be eligible for public supports such as food stamps, the Children's Health Insurance Program and others. Present immigration law bars non-citizens from receiving cash assistance from federal programs and imposes a five-year waiting period for new immigrants before they can enroll in Medicaid (although states have the option to cover them anyway). However, food stamps aren't considered cash assistance. Additionally, children, because they are a vulnerable population, should be eligible for Medicaid/CHIP regardless of immigration status.
3. The U.S. would need to make exception for children who would otherwise be stateless. Oddly, the U.S. has not acceeded to the 1961 U.N. Convention on the Reduction of Statelessness. Were the U.S. to modify jus soli, it should also sign the Convention. Stateless people are extremely vulnerable because they have difficulty accessing all social services and benefits in their home countries and their countries of residence.
4. Any changes to jus soli would need to come with comprehensive immigration reform.
These changes to U.S. public policy should actually be considered no matter what changes are made to jus soli. They are consistent with international treaties that the U.S. has signed on to or should sign on to.