Trade union membership is a vital element in assessing the strength and status of a trade union. Its growth is attributed to the advancement in the National industrial relations system. Therefore, this focuses on identifying the factors that contributes the factors responsible for declining trade union membership. The respondents of this study are unionized employees representing five different sectors. The data is analyzed using multiple regression. The findings indicate that all the factors studied contribute to decline in trade union membership. This includes trade union internal factors, employer hostility and industrial relations climate. Thus, the actors of industrial relations system should pay attention in protecting the rights and welfare of the workers.