Is it permissible to impose a financial penalty on those who are late in paying their voluntary blood money (Diyya) fund subscriptions, knowing that the penalty is to ensure commitment and the subscription is not mandatory?

Establishing family cooperative funds to help those in need is a good deed, and participation in them should be optional, not compulsory. It is not permissible to impose a financial penalty on anyone who delays paying the annual subscription, because that is taking money without the person's willing consent, makes charitable work compulsory, and is considered a financial chastisement (ta'zir), which is the right of the legitimate ruler. Priority in assistance can be given to those who commit to paying.