Esther 1:16 - 18

"Then Memucan replied in the presence of the king and the nobles, 'Queen Vashti has done wrong, not only against the king but also against all of the nobles and the peoples of all the provinces of King Xerxes. For the queen's conduct will become known to all the women, and so they will despise their husbands and say, "King Xerxes commanded Queen Vashti to be brought before him, but she would not come." This very day the Persian and Median women of the nobility who have heard about the queen's conduct will respond to all the king's nobles in the same way. There will be no end of disrespect and discord.'" NIV translation

So, the king's expert doesn't quote any law that the queen broke but points out the fact that all of the men in the kingdom will lose control of their wives. The expert also points out that it is going to start immediately so they have to act promptly.

Esther 1:19

"'Therefore, if it pleases the king, let him issue a royal decree and let it be written in the laws of Persia and Media, which cannot be repealed, that Vashti is never again to enter the presence of King Xerxes. Also let the king give her royal position to someone else who is better than she.'" NIV translation

Memucan continues to counsel the king by giving him an answer to his problem. That answer is for the king to replace the queen with another. Up to this point, it doesn't seem like these events have anything to do with God or His people. But, you can almost feel God at work behind the scenes putting His people in place. The same thing is true in our lives today as we may not see all that God is doing but we can be assured that He is at work looking out for His children.