put one's foot down 坚决反对某人想做的事。

【例句】
That's it, I am marching over there and putting my foot down with Max.
够了，我要杀过去跟Max谈判。

Mother let us go to the party, but when it came to staying overnight, she put her foot down firmly.
母亲允许我们去参加晚会， 但要说到过夜，她可决不答应。