Clothing of seminarians is regulated by the particular diocese or order of the seminarian and the seminary in which he lives. It is common practice in many seminaries that seminarians wear clerical attire within the confines of the seminary. Whether a cassock would be acceptable attire within the seminary is up to the seminary.
When it comes to seminarian attire when within their own diocese, this is a much more diverse group of regulations. Some dioceses permit seminarians to wear clerical collars, some dioceses forbid it and require black suit and tie, other dioceses forbid clerical collars but have no “dress code.” Religious congregations would have their own set of regulations, or failing that would leave the decision up to a particular authority within the local congregation.
