Catechism of the Catholic Church §903 — excerpt
Lay people who possess the required qualities can be admitted permanently to the ministries of lector and acolyte. When the necessity of the Church warrants it and when ministers are lacking, lay persons, even if they are not lectors or acolytes, can also supply for…
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Also cites: CIC, can. 230 # 1 · CIC, can. 230 # 3