Ps were employed in New Hampshire during the 1970 tax year and were subject to the New Hampshire Commuters Income Tax. That Tax imposes a tax on nonresidents' New Hampshire-derived income in excess of $2,000. The New Hampshire tax is reduced to the amount of the tax that the State of residence would impose. Employers are required to withhold 4% of the nonresident's income, even if his home State would tax him at less than the full 4%. Ps petitioned the New Hampshire Superior Court for a declaration that the tax violates the Privileges and Immunities and Equal Protection Clauses of the Constitutions of New Hampshire and of the United States. The cause was transferred directly to the New Hampshire Supreme Court, which upheld the tax. Ps appealed and the Supreme Court granted certiorari. No resident of New Hampshire is taxed on his out-of-state income. Nor is the domestic earned income of New Hampshire residents taxed. The State taxes only the incomes of nonresidents working in New Hampshire.