Walker v. Pennsylvania was a United States Supreme Court case that addressed the issue of whether a state could impose a tax on a railroad company that was chartered by another state. The case was brought by the Pennsylvania Railroad Company, which was chartered by the state of New Jersey. The company argued that the tax imposed by Pennsylvania was unconstitutional because it violated the Privileges and Immunities Clause of the United States Constitution. The Supreme Court held that the tax was constitutional because the company was not being discriminated against based on its status as a foreign corporation. The Court reasoned that the tax was imposed on all railroads operating in Pennsylvania, regardless of their state of origin. The Court also noted that the tax was not excessive and did not place an undue burden on the company. The Court's decision in Walker v. Pennsylvania established that states have the right to impose taxes on foreign corporations operating within their borders, provided that the taxes are not excessive and do not discriminate against the foreign corporation. This decision has been cited in numerous subsequent cases involving the taxation of foreign corporations.

Justice Harlan delivered the dissenting opinion in Walker v. Pennsylvania, arguing that the state of Pennsylvania had violated the Fourteenth Amendment by denying a black man his right to vote. He argued that while states have broad authority to regulate voting rights, they cannot do so if it results in discrimination against any race or class of citizens. In this case, he noted that there was no dispute as to whether or not Walker was qualified under existing laws and regulations; rather, he had been denied his right solely on account of his race. As such, Justice Harlan concluded that this constituted an unconstitutional violation of equal protection under the law and should be overturned accordingly.