Ye fast for strife and debate. Delitzsch explains, "When fasting, they are doubly irritable and ill tempered; and this leads to quarrelling and strife, even to striking with angry fists." This is quite a possible explanation.
Or there may have been two parties, one for, the other against, fasting; and those who practised fasting may have done it, as some preached Christ, "of envy and strife" (Philippians 1:15)—to provoke the opposite side.
Ye shall not fast as ye do this day, to make your voice to be heard on high; i.e. "ye must not fast as ye do at present, if ye would have your voices heard in heaven." God will not hear the prayer of which such a fast is the accompaniment.