Sorry, it was divorce and remarriage, although one could make the case for multiple wives. Passage hits on other things in this thread too.
Matthew 19: 3-9
3*And Pharisees came up to him and tested him by asking, "Is it lawful to divorce one's wife for any cause?" 4*He answered, "Have you not read that he who created them from the beginning made them male and female, 5*and said, 'Therefore a man shall leave his father and his mother and hold fast to his wife, and the two shall become one flesh'? 6*So they are no longer two but one flesh. What therefore God has joined together, let not man separate." 7*They said to him, "Why then did Moses command one to give a certificate of divorce and to send her away?" 8*He said to them, "Because of your hardness of heart Moses allowed you to divorce your wives, but from the beginning it was not so. 9*And I say to you: whoever divorces his wife, except for sexual immorality, and marries another, commits adultery."
I see that as a rebuke of divorce (except in cases when the marriage was unlawful or the wife is unfaithful), but not a specific rebuke of polygamy.
In a lawful situation, why could it not be that God joined a man and woman, made them one flesh, then the man married again, and God made them one flesh?
The only place I have found polygamy rebuked, in the New Testament, is from Paul in discussing the requisite lifestyles of deacons.