You fast with contention and strife to strike viciously with your fist. You cannot fast as you do today and have your voice be heard on high.
KJV
Behold, ye fast for strife and debate, and to smite with the fist of wickedness: ye shall not fast as [ye do this] day, to make your voice to be heard on high.
ASV
Behold, ye fast for strife and contention, and to smite with the fist of wickedness: ye fast not this day so as to make your voice to be heard on high.