ASLEF's case was that the union had been prevented from expelling a member due to his membership of the BNP, a political party which advocates views inimical to its own, and that this was an infringement of freedom of association. The nature of the argument is that the United Kingdom's law (i.e. s.174 of TULRCA 1992) which required ASLEF to take back Lee into union membership or face compensation payments, violates union members' freedom of association. So ASLEF was now suing the UK government (rather than Lee).