"An employee also has the right not to have action short of dismissal taken against him for the purpose of enforcing a requirement ... that, in the event of his not being a member of any trade union, or of a particular trade union or one of a number of particular trade unions, he must make one or more payments."
" ... any deduction made by an employer from the remuneration payable to an employee in respect of his employment shall, if it is attributable to his not being a member of any trade union or of a particular trade union ... be treated as action short of dismissal taken against him for the purpose of enforcing a requirement of a kind mentioned in that subsection."
"On a complaint under section 146 it shall be for the employer to show the purpose for which action was taken against the complainant."