The prohibition against imports in, and the penalty of forfeiture of, certain vessels from countries which discriminate against American vessels provided for in subsections 2 and 3 of paragraph J, section IV, Tariff Act of 1913, as amended by the act of March 4, 1915 (19 U.S.C. 130,131,shall. (See also §§ 4.20(c) and 159.42 of this chapter.)