So where in the following (canon law) does it say when ministering?
"… The National Conference of Catholic Bishops, in accord with the prescriptions of canon 284, hereby decrees that without prejudice to the provisions of canon 288, clerics are to dress in conformity with their sacred calling.
In liturgical rites, clerics shall wear the vesture prescribed in the proper liturgical books. **Outside liturgical functions, a black suit and Roman collar are the usual attire for priests. The use of the cassock is at the discretion of the cleric.
**
In the case of religious clerics, the determinations of their proper institutes or societies are to be observed with regard to wearing the religious habit. …"
You can also find various exhortations. For example, there is this from John Paul II in Vita consecrata: “Since the habit is a sign of consecration, poverty and membership in a particular Religious family, I join the Fathers of the Synod in strongly recommending to men and women religious that they wear their proper habit, suitably adapted to the conditions of time and place.**Where valid reasons of their apostolate call for it, **Religious, in conformity with the norms of their Institute, may also dress in a simple and modest manner, with an appropriate symbol, in such a way that their consecration is recognizable. Institutes which from their origin or by provision of their Constitutions do not have a specific habit should ensure that the dress of their members corresponds in dignity and simplicity to the nature of their vocation” (n. 25).
Does that sound like canon law is allowing for casual attire for days off?