First Council of Nicaea, Canon XVII

Forasmuch as many enrolled among the Clergy, following covetousness and lust of gain, have forgotten the divine Scripture, which says, “He hath not given his money upon usury,” and in lending money ask the hundredth of the sum [as monthly interest], the holy and great Synod thinks it just that if after this decree any one be found to receive usury, whether he accomplish it by secret transaction or otherwise, as by demanding the whole and one half, or by using any other contrivance whatever for filthy lucre’s sake, he shall be deposed from the clergy and his name stricken from the list.

Translation: Henry R. Percival, The Seven Ecumenical Councils, NPNF II.14 (1900), via CCEL.