. . . "ure of the employee to tender the periodic dues, initiation fees, and assessments (not including fines and penalties) uniformly required as a condition of acquiring or retaining membership. 64 Stat. 1238, 45 U.S.C. 152, Eleventh. [Footnote 10] See the provisions of the constitutions of the Brotherhood of Maintenance of Way Employees, the Brotherhood of Railway Carmen of America, and the Internati" . .