Here Keynes is arguing that a given labor group’s negotiations around money wages serves to determine that groups relative real wages, that is, relative to other labor groups.
unresolved Is he also saying that a labor group’s settlement for lower money wages means that the group also suffers a decrease in real wages, but also that this decrease contributes to a trend of overall increase in real wages across labor groups?
In other words, the struggle about money-wages primarily affects the distribution of the aggregate real wage between different labour-groups, and not its average amount per unit of employment, which depends, as we shall see, on a different set of forces. The effect of combination on the part of a group of workers is to protect their relative real wage. The general level of real wages depends on the other forces of the economic system.