The Saltonstall v. Birtwell case in 1896 revolved around a dispute over the interpretation of customs duties on imported goods. The plaintiff, Saltonstall, was an importer who claimed that he had been charged excessive duties by the defendant, Birtwell, a collector for the port of Boston. The specific issue at hand was whether certain types of iron or steel wire should be classified as "iron" or "steel," which would affect their duty rate under existing tariff laws. The Supreme Court ruled in favor of Birtwell and upheld his classification and subsequent charges on these imports based on technical definitions provided by experts during trial proceedings.

The dissenting opinion in the Saltonstall v. Birtwell case argued that the court majority had erred in its interpretation of the law and constitutionality regarding taxation on bonds issued by foreign governments. The dissent contended that such bonds, held by American citizens, should not be exempt from federal income tax as they were a form of property or wealth within U.S jurisdiction. It was further asserted that this exemption created an unfair advantage for wealthy individuals who could afford to invest in these types of securities over average taxpayers. Additionally, it was pointed out that there is no constitutional provision explicitly prohibiting Congress from taxing income derived from any source whatsoever; hence, excluding foreign government bond interest from taxable income contradicted legislative intent and precedent.