In a follow-up to this post, I should note that the doyen of Jewish business ethics, R. Dr. Aaron Levine, has published on the issue of the Minimum Wage -- "The Interface Between Economics and Halakhah: The case of Minimum Wage Legislation" in The Torah U-Madda Journal 1 (link), which was expanded into "Minimum Wage Legislation-A Halakhic Perspective" in Tradition 24:1 (link) and published as a chapter in his book Economic Public Policy and Jewish Law.
R. Levine argued against the Minimum Wage because of its negative economic impact. His article(s) was written in 1988. The author of the paper on the Living Wage wrote an appendix in which she quotes extensively from economic studies which claim that case studies have shown that Minimum and Living Wages do not have a negative impact. If that is correct, and I am in no position to judge whether it is or is not, then R. Levine would probably support a Minimum (or Living) Wage.
Precisely this was argued by Jerold L. Waltman in his book The Case for the Living Wage (which I haven't read and only found via Google Books), pp. 43-44:
In fact, Aaron Levine has said that "the stated goal of minimum wage legislation, ensuring the working poor a 'living wage,' is an objective Halakah [Jewish law] would fully embrace." He goes on to argue, it is true, that the minimum wage is counterproductive because it leads to unemployment. However, if this proposition could be refuted, as I hope to do in Chapter 7, then the Jewish law, and even Levine, would stand clearly behind a living wage...I don't know whether R. Levine accepts the economic argument that a Minimum or Living Wage is not damaging.
UPDATE: See this post for an update: link