The canon prohibits ordaining people from other dioceses without the consent of their bishops. The canon mentions ordaining clerics (i.e. promoting them to a higher grade) and also laymen. It can be presumed that this concerned rather higher clerical grades, including the presbyterate, since ordaining to lower grades probably would not cause arguments: it is also difficult to see how there could be a pressing need for e.g. an ostiarius.
What were the reasons for prohibiting ordaining people in other dioceses? Firstly, not to allow the situation in which someone deemed unsuitable for an ordination by his bishop simply went to another. Secondly, there might have been an issue of the disproportion of the number of clergy; candidates might have been preferring to go to bigger cities. See also  about the letters needed to accept communion in other dioceses.
Bishop Gratus mentioned Canon 13 (16 in the Latin version) of the Council of Sardica (AD 343/344).