I will add to your yoke, i.e. make it heavier and stronger, both to punish your petulancy, and to curb and restrain you from seditious attempts. With scorpions, i.e. with such whips as will sting you like scorpions: if you proceed in these courses, I will most severely punish you for it.
Related Commentaries of 1 Kings 12:11
1 Kings 12:11
11 And now whereas my father did lade you with a heavy yoke, I will add to your yoke: my father hath chastised you with whips, but I will chastise you with scorpions.