Can the domicile parent not allow the nondomicile parent no contact with the children

Not and No. Your double negative infers Yes but your question infers No. What is it? If you mean No contact, custodial papers should state so. If no papers, no, you cannot prohibit contact as the children are their's too.

What are the reasons for the no contact? Has there been any decisions by the courts? Is the other party a true danger to the child and if so how do you know this ?

Bottom line is the domicile parent has to abide by the court order. So what does the court order say? If the court order provides for visitation then the domicile parent is required to have the childe ready for the visit according to the terms of the court order or face court sanctions.

Only the court can order no contact and that is seldom done unless they are a danger. And even then they often can get supervised visits.

The non-custodial parent should contact the court immediately if the custodial parent refuses to permit court ordered visitation.