All stories uploaded to the Archive must be submitted by the author. There are fandoms out there where stories are picked up by Archives themselves when they are posted. Which usually leads to frantic 'don't do it' notes from authors at the bottom of stories.
But we've always approached it from the other direction - that the onus is on the author to choose if they want their story archived, rather than the archive doing it by default, without their permission.
LabRat
