The affix ṭa comes after the verb kṛñ 'to make' when the word karma is in composition with it and the sense of the word to be formed is that of wages.,
The word भृति means service for hire, wages. The word कर्म does not mean the grammatical object but the word-form कर्म; as कर्मकरः 'a hired labourer' (not a slave); otherwise the affix is अण्; as कर्मकारः 'an artisan'.,