If the couple did not consummate the marriage (by having sexual intercourse)
If the couple have only had sex using contraception, they may be able to get an annulment because they have not been open to receiving children from God
If the couple were forced to get married, or had pressure placed on them to get married, their marriage is not valid
If either member of the couple was still tied to a previous marriage, or to other vows, their new marriage would not be valid