Nonimportation Act, a law passed by the U.S. Congress in April, 1806, to forbid the importing of certain goods from Great Britain, in retaliation for British interference with American shipping. It was suspended for a year in December, 1806, in the hope that negotiations could end the interference. It became effective again on December 14, 1807, but later that month was superseded by the Embargo Act of 1807.