the brother of a man who died without children is permitted and encouraged to marry the widow. However, if either of the parties refuses to go through with the marriage, both are required to go through a ceremony known as halizah, involving a symbolic act of renunciation of their right to perform this marriage.
So, permitted and encouraged, but not forced into it. Except by god it seems.
It was actually the law to do that, IIRC. https://en.wikipedia.org/wiki/Yibbum
Well the article says that
So, permitted and encouraged, but not forced into it. Except by god it seems.