lay down the law
1．give strict orders下命令；严令
He could usually be found in the centre of a small group of people to whom he was laying down the law．我们常看到他在一小群人当中发号施令。
2．speak severely or seriously about a wrong doing；scold严厉斥责；呵斥
The principal called in the students and laid down the law to them about skipping classes．校长集合学生严责他们逃课。
Father is laying down the law to the children again； I wonder what they've done now．父亲又严厉地训斥孩子们了，不知道他们现在又干了什么事。