United States. Department of the Treasury. "Cast Iron Soil Pipe and fittings from Poland, June 6, 1967," in United States. Department of the Treasury. "Volume 158," Press Releases of the United States Department of the Treasury (June 1, 1967 - August 29, 1967) : 19-20. https://fraser.stlouisfed.org/title/6111/item/587001/toc/540716 , accessed on May 19, 2024.