For many years, our Diocesan Directives have included this provision:
“No priest of the Diocese or visiting missionary is to take up any collection personally during a liturgical celebration. No special collection by visiting priests, nuns, brothers of representative of Catholic projects may be taken up without a letter of approval by the Bishop. Similarly, the pulpit is not to be used for any appeal for support, financial, or otherwise, for any other than a local parish project without the approval of the Bishop.”
Consequently, pastors should negotiate in advance a set stipend with anyone preaching a parish mission. Any collection or “free will offering” during the course of a parish mission goes to the parish.