§1. When it can be done in the judgment of the diocesan bishop, a procession through the public streets is to be held as a public witness of veneration toward the Most Holy Eucharist, especially on the solemnity of the Body and Blood of Christ.
§2. It is for the diocesan bishop to establish regulations which provide for the participation in and the dignity of processions.
Source: Code of Canon Law (Vatican.va)