The paper in question describes a collaborative study of several datasets (not all previously published). A putative referee was asked to review the paper and declined. However, this led to a written complaint asserting that (s)he should be an author as (s)he had made a significant contribution to some of the work described in the paper.
After promising comments from referees, the existing authors were invited to resubmit, but asked to resolve the authorship issue before resubmission. The paper has now been revised and resubmitted, but is currently "stalled". The authors say that the individual making the complaint does not deserve to be an author. The complainant has still not seen the paper, but continues to feel strongly that (s)he should be an author.
The institution at which the work in question was done has been contacted, and is investigating. A related complaint has been made previously, and does not appear to have been resolved satisfactorily—there are various arguments for and against the claim for authorship and plans are afoot to convene a panel with the appropriate attributes (independence, familiarity with legal issues, and scientific culture, etc). One co-author has a joint appointment at two institutes, and so both directors will need to be involved in the process.
Is the way in which the putative referee obtained confidential information objectionable?
Have the authors acted improperly in not sending the paper to the complainant?
How best can we now balance the interests of the authors, complainant (the complaint may be genuine or malicious), and indeed other people who might wish to be authors too?
What should be done regarding possible publication?