The power to award preference to unionists pursuant to the Commonwealth Con ciliation and Arbitration Act, 1904 is potentially of great importance to the trade union movement. When such a power is exercised it may extend to union members an advan tage over non-unionists across a broad range of employment rights, including engage ment, promotion, taking of leave and retrenchment. It is argued that the power to grant preference has been misunderstood and misapplied by those responsible for its implementation, and that unionists have thereby been deprived of benefits to which they were legally and ethically entitled. It is argued further that the supposed 'principles' adopted in preference cases have been inadequately identified and analysed. In practice one principle has prevailed: preference would be refused unless an employer could be shown to be actively discriminating against union members. Opportunity for a revision of the principles applicable in preference cases arose with the passage of the 1947 amendments to the Conciliation and Arbitration Act. However, the impact of these amendments was to all intents and purposes negated by the High Court's decisions in R. v. Wallis and R. v Findlay. A disinclination to revise past practice in preference cases and to take a more expansive approach to the issue led to the complete demise of federal union interest in preference awards by the late 1960s. © 1987, Sage Publications. All rights reserved.