Though you must have already a list of 'older' works, Braverman's Labor and
Monopoly Capital (1974) must still be one of starting point for the subject.
My book, The Basic Theory of Capitalism (Macmillan, Barnes and Noble, 1988)
also contains some theoretical contributions (in chap5, 6) on how to treat
labour as a basis for class relations.
By the way, a series of arguments in OPE-L on abstract labour, in my
feeling, would have a different approach from the view of my (unoist)
contributions.
Makoto