Today, 639 years ago, in the year 1381, the Rabbinate in Mainz, established a cherem, for one who is obliged to give his sister in law Chalitzah – and he denies to give it to her.
A woman whose husband passed away without having children, his brother must either marry her or give her Chalitzah in Beis Din. Thereafter she is free to get remarried.
It was common practice to withhold Chalitzah in order to extort money from the widow. Therefore the Rabbanim set this cherem in Place.
Source: Maharam Minz 10