The ties between social democratic parties and trade unions in recent years have been stretched almost to breaking point. Drawing on evidence from the experience of Australia and Britain, this article argues that a turning point in the deterioration of the relationship was the collapse of the post-war economic boom. This event was important because it ruptured the economic foundations of the policy base of social democracy and led to the adoption by social democratic parties of a pro-business neo-liberal policy framework aimed at restoring rates of investment and profitability. In turn, this new policy emphasis necessarily threatened the interests of organised labour. The current tension in relations is therefore not merely a reflection of the pressures associated with social democrats being in government. Rather, it is rooted in the gradual decline of the health of capitalism since the 1970s - a trend unlikely to be reversed in the near future.