Final answer:
The Mann-Elkins Act was not passed under President Wilson but rather under President Taft in 1910. The Underwood Tariff, Federal Reserve system, and Clayton Anti-trust Act were a part of Wilson's New Freedom agenda.
Step-by-step explanation:
The piece of progressive legislation that was not passed under President Woodrow Wilson is: a. Mann-Elkins Act. Instead, the Mann-Elkins Act was enacted under President William Howard Taft in 1910, which extended the regulatory powers of the Interstate Commerce Commission. On the other hand, the other options listed, b. Underwood Tariff, c. Federal Reserve system, and d. Clayton Anti-trust Act, were indeed passed under Wilson as parts of his New Freedom agenda, which aimed to address issues related to tariffs, the banking system, and monopolistic business practices.