Meet Mormon Missionaries website says so:
According to Jacob, only when God commands it can people practice polygamy and He will do so in order to raise more children. The Mormons practiced polygamy as commanded by God and did so for a limited time until God commanded the Prophet to end the practice.
Earlier on that same page he condemns the Muslims for their practice of polygamy:
The Book of Mormon clearly explains that sometimes God commands people to practice polygamy and other times he forbids it since only very righteous people can handle it.
I find it odd that LDS Inc is allowing such websites to proliferate. Information like this will not be found on Mormon.org or LDS.org.. Won't this just confuse the unwitting possible investigator?