The Order is commonly mentioned by various Ascalonian Necromancers although it isn't given any name other than "the Order." It is likely that the Order is the predominant Necromancer organization in Ascalon, as most known prominent Ascalonian Necromancers are currently or were formerly members. More than just Necromancers are in the Order, however, as at least one Elementalist is in it.
It is hinted in the quest Renegade Necromancer that the Order is around to prevent abuse of Necromancy. Elementalist Aziure's dialogue and the quest The Elementalist Experiment implies that they look into "Time, Life, Truth" and learning new magic.