The phrase, the karma of untruthfulness, is taken from a series of lectures by Rudolf Steiner, and it can be understood to mean that untruthfulness - lying, dishonesty, deliberate misleading - carries a 'karma'.
This I mean in a Christian sense (and one different, in several important respects, from that implied by several of Steiner's metaphysical and empirical assumptions):
Sin necessarily carries a cost; and untruthfulness without repentance is a sin; and un-repented sin is the prime path of a soul, to self-chosen damnation.
The karma of untruthfulness operates at the level of our Western civilization, at regional and national levels, for social institutions of all sizes; and, most importantly, for individual human beings.
We already, and increasingly, live-by untruthfulness: untruthfulness structures the main aspects of our public life, policy, and discourse; and (ever-more-so) our private discourse - even within marriages, families, and among close friends.
And, at its core; untruthfulness structures the basic reality assumptions (metaphysics) and thinking of many or most Western people.
The usefulness of the term karma is in its unavoidability; the idea that the costs are intrinsic.
This is not a matter of costs coming if people 'don't get away with' their lies. It is that our 'world' of untruthfulness brings its own punishment immediately and necessarily - as well as cumulatively through time.
A world in which people choose to believe and live-by that which is false is already a world that is self-damned; and self-damnation manifests at every level; because it is a choice of negation, of hostility to divine creation - a choice of meaninglessness, purposelessness, and chaos.
Here and now - truthfulness is of supreme importance; a truthfulness that needs to extend down to the roots of our understanding of the world itself, as well as to the minutiae of everyday living.