The Privileges and Immunities Clause or Comity Clause of the U.S. Constitution, Article IV, Section 2, Clause 1, protects citizens of one state who travel to another state. This Clause protects their right to travel, access to courts, and equal treatment for nonresidents. This clause reads, "The Citizens of each State shall be entitled to all Privileges and Immunities of Citizens in the several States."
There is a Privileges or Immunities Clause in the Fourteenth Amendment to the U.S. Constitution, but it has been almost meaningless for over a century. In the Slaughter-House Cases (1873), the U.S. Supreme Court held that this clause protects only those rights "which owe their existence to the Federal government, its National character, its Constitution, or its laws." Examples include the right "to come to the seat of government, ... the right of free access to its seaports, ... to the subtreasuries, land offices, and courts of justice in the several States ... to demand the care and protection of the Federal government ... when on the high seas or within the jurisdiction of a foreign government, ... to peaceably assemble the petition for redress of grievances, the privileges of the writ of habeas corpus, ... [t]he right to use the navigable waters, [and the right to] become a Citizen of any State of the Union by a bona fide residence therein, with the same rights as other citizens of that State."
In no decisions between 1873 and 1999, except for one decision that was then overruled, did the Privileges and Immunities Clause of the Fourteenth Amendment make a difference. But in Saenz v. Roe (1999), the Supreme Court did invoke the Privileges and Immunities Clause of the Fourteenth Amendment to invalidate a California law that defined welfare benefits for new residents and California citizens at the (lower) level provided by their former state for their first year in California. The Court found this discrimination to violate one of the privileges and immunities of being an American citizen.
Justice Clarence Thomas has suggested reviving the Privileges and Immunities Clause. In a dissent he wrote that "the demise of the Privileges or Immunities Clause has contributed in no small part to the current disarray of our 14th Amendment jurisprudence." To clarify things, "I would be open to re-evaluating its meaning in an appropriate case."