Many libertarians are sceptical about the idea of social justice, citing Hayek's argument that social justice is a mirage. Indeed, recently David Friedman had a debate with Jason Brennan, John Tomasi and Matt Zwolinski of the Bleeding Heart Libertarians blog over whether the concept even had a clear meaning. My own view is that social justice is just justice writ large, with particular focus on distributive issues like equality, priority and sufficiency.
Many classical liberals were deeply interested in questions of distributive justice, including Adam Smith, who made his name as a moral philosopher, and often focused on the damaging effects mercantilist and other interventionist policies had on the worse-off. Barry Stocker has recently posted the text of three very interesting talks he gave in Istanbul on the subject of Smith and distributive justice. Stocker highlights the ways in which Smith laid the blame for unjust distributions of society's goods at the state's door:
The cause [of unjust distributions] is largely the activity of the state rather than the results of markets being left free of state legislation and government schemes. Smith sees injustice as resulting from collaboration between merchants in the same sector, but sees this as more the consequence of state intervention than of free commerce. The state enabling, encouraging and even requiring enterprises to form corporate bodies (such as local chambers of commerce in Britain) in the same sector is the biggest reason for merchants conspiring against the public. That is the source of the famous quotation about merchants conspiring against the public, though that quotation is often used to support demands for increased state regulation.
And Stocker also highlights how Smith's concern for social justice did not translate into calls for redistribution; he believed that a good overall institutional structure would generate desirable distributional outcomes:
One of the problems with Smith commentary is that admirable scholars and political theory thinkers, like Rasmussen and Fleischacker, who are disposed favourably to a theory of redistributive justice see it in those elements of Smith which express a wish for distributive justice. There is distributive justice in Smith in the sense that he favours the distribution that emerges from freedom in economic activities, and in the state measures he favours to benefit the poor rather than the rich. However, that is not the same as the kind of belief in a predetermined pattern of distribution of justice which Rawlsians, or egalitarian liberal favour, at the extreme a completely flat distribution as argued for by G.A. Cohen and which is in the basic assumptions of Habermas‘ thought on norms, ethics, and discourse.