By looking up the Alabama song up with the proper title "40 Hour Week (For a Livin')" it seems to have been written by Dave Loggins and Don Schlitz (of "The Gambler" fame), and recorded in 1984.

In this case "working man" is used as a synonym to "blue collar" worker.

It's always seemed odd that Merl Haggard is famous for his "Working Man's Blues", but he does not seem to have worked a day in his life (unless you consider music work).