The prince threatens that if they don't stop fighting then they will have to leave Verona or be punished by death.
What Threat Does The Prince Make To Lord Montague And Lord Capulet In Romeo And Juliet?
Escalus, Prince of Verona. (a part Shakespeare wrote for himself), tells the heads of the two powerful families of Montague and Capulet, that after exiling Romeo for the murder of Tybalt, he "has an interest in your hate's proceeding; / My blood for your rude brawls doth lie a- bleeding / But I'll amerce (punish) you with so strong a fine/ That you shall all repent the loss of mine/ I will be deaf to pleading and excuses/ Nor tears nor prayers shall purchase out abuses/ Therefore, use none, let Romeo hence in haste,/ Else when he is found, that hour is his last, (sentenced to death).