Imposition of tax

There is hereby imposed on every rail employer for each calendar month an excise tax, with respect to having individuals in his employ, equal to 4 percent of the total rail wages paid by him during such month. There is hereby imposed on the income of each employee representative a tax equal to 4 percent of the rail wages paid to him during the calendar month. The rail wages of an employee representative for purposes of paragraph (1) shall be determined in the same manner and with the same effect as if the employee organization by which such employee representative is employed were a rail employer. The tax imposed by this section shall not apply to rail wages paid on or after the 1st day of any calendar month if, as of such 1st day, there is—