We have a formal process here, which has multiple phases:
According to section 2.5 of our Terms of Service, a Primary Author can initially act unilaterally in a number of ways, "including but not limited to the original division of royalties amongst co-authors, any subsequent change in the division of royalties, the granting or the revocation of co-authorship status", etc (emphasis added).
If a Primary Author does anything which leads someone else to believe that a case of copyright infringement has occurred, we have a formal "Notification of Infringement" process for claims of copyright violation set out here. We recommend you read the whole page to understand how the process works, but briefly, you would file a formal Notification of Infringement by mail or by email.
Upon receipt of the Notification of Infringement, we would evaluate it and determine whether, and how, to act.
We may also attempt to notify the Primary author, who would be entitled to file a Counter-Notification.
Upon receipt of any Counter-Notification, we would evaluate it and determine whether, and how, to act.
Our intention is to have a fair and clear process here. However, we really want our authors to sort these types of things out amicably between themselves...