The Seventh Ecumenical Council.  The Second Council of Nice 23Canon XIV.

That no one without ordination ought to read in the ambo during the synaxis.

That there is a certain order established in the priesthood is very evident to all, and to guard diligently the promotions of the priesthood is well pleasing to God. Since therefore we see certain youths who have received the clerical tonsure, but who have not yet received ordination from the bishop, reading in the ambo during the Synaxis, and in doing this violating the canons, we forbid this to be done (from henceforth,) and let this prohibition be observed also amongst the monks. It is permitted to each hegumenos in his own monastery to ordain a reader, if he himself had received the laying on of hands by a bishop to the dignity of hegumenos, and is known to be a presbyter. Chorepiscopi may likewise, according to ancient custom and with the bishop's authorization, appoint readers.