ASK FATHER: Can the bishop forbid the cassock?
From a priest…
QUAERITUR:
I am trying to find an answer to the question of whether a bishop can prohibit a priest from wearing the cassock. Below is the pertinent section from the Directory for the Ministry and Life of Priests which mentions the local Bishops’ Conference and its norms…etc… [Edited out for reasons of brevity.] It seems to imply that the cassock is normative and can always been worn even if the conference offers other options… [It indeed does imply that.]
Is this right? [Yes.]
If a priest is in good standing, has not done, nor is doing, anything to bring shame on his office publicly when wearing said cassock, can a bishop simply say, “I don’t want you wearing it…” ?, especially if the Conference has not issued any specific norms itself.
Of course a bishop can’t prohibit a priest from wearing a cassock!
The cassock is the Church’s expectation of what a priest wears, as you correctly discern from the Directory. It is listed first and it is the default garment for the Roman priest.
However, Holy Church, in her generosity, also wishes to accommodate the transitory styles of culture (presuming that what we see these days can truly be called “culture”). For example, during a time of Know Nothing anti-Catholicism in these USA the Council of Baltimore determined that priests shouldn’t wear the cassock when out and about in the streets, but rather should wear the clerical collar and the frock coat. 
I’ve only known one cleric who wore the frock coat in accordance with that Council btw. Dapper, but eccentric.
According to the dictates of common sense, the sensible priest may wear other clothing than the cassock, clothing suited to the task at hand. He may wear a black suit and black shirt with clerical collar. He may wear a union suit when crawling under the rectory to fix the pipes. He may wear a modest bathing suit when swimming. He may wear sweatpants and a jersey when stretched out on the rectory couch to watch a football, soccer, cricket, or rugby match. He may wear tactical camouflage whilst hiding in the forest waiting for the elusive fourteen-point buck. He may wear a frightening clown suit when lurking in the woods near a convent of polyester-pantsuited nuns holding an “I’m with Hillary” rally.
I’ve never seen the sense in wearing the cassock to, for example, climb ladders to change bulbs, to wash a car, or to play hockey in a serious way. Yes yes we’ve all seen the photos. And, yes yes, I can see shooting some baskets with the kids on the playground for a few minutes, but… sheesh.
A bishop, being a creature with free will, can certainly say to a priest, “Father, I don’t want you wearing a cassock”. At that point the priest would be within his rights to answer his Ordinary, respectfully, saying, “Your Excellency, thank you so much for your opinion, but that is above your pay grade.”
If the bishop is a humorless liberal – as as all liberals are… that was redundant – you, the prepared priest, might wear a thin cassock over your normal cassock. When Bishop Fatty McButterpants says that he wants you to stop wearing a cassock, immediately take the outer cassock off, revealing your regular cassock. “Yes, Your Excellency, right away, Your Excellency!”
Of course, you must subsequently be reconciled with being a parochial vicar for a considerable amount of time to Fr “Just Call Me Bob” at Engendering Togetherness Community of Welcome, or serving as the chaplain to the Sisters, Servants of Our Lord’s Sacred Tambourine.
Bottom line, no, a bishop has no right whatsoever to forbid the quintessential priestly garment.
