Occasionally it happens that a referee suggests citing their own papers in a review. This may be a problematic practice, since there is a thin line between appropriate and inappropriate recommendations, and since it could help the authors identify reviewers.
As an editor, what should I do when I see it happening in a paper I am handling? Please base your answers on your own experience or on official recommendations.
This is very simple: You are the editor. This is not a problematic practice but just part and parcel of the review process.
If you are the editor, you get to make the decision. (I assume that there is a way to handle complaints about your decision, as most journals / professional organizations provide that.) A referee is obliged to check whether references are suitable. You as the editor in charge selected the referees because they knew the field, so it should be relatively common that the referee also has published in the field. Objectively, there will be cases where a referee's publication should be cited and maybe discussed into the revised version of the paper. Subjectively, a referee will sometimes err and occasionally sin by demanding that one of their publications be discussed. (Also, there are predatory journals who will ask a paper to cite other papers from the same editorial group, but this is not our topic.) This is where your job as editor comes in. You need to make a decision:
You can tell the author that they might want to consider the request but that acceptance will not depend on their decision.
You can tell the author that they definitely should include the reference and discuss the connection. You can also invite them to send you a message discussing how they see it.
You can tell the author that the paper is rejected because it duplicates results that the referee already published.
And there are of course more possible outcomes.
However, you are the editor and you have to make the final decision. If you feel uncomfortable or need help, there should be other editors or maybe a senior editor to ask for advice. You as editor are the guardian of scientific integrity.
You would be a fool if you invite someone to review a paper and then do not listen to what they say. But you are not the reviewer's peon.
If you feel that the reviewer is revealing their identity, you can redact what they are saying or play this back to the reviewer if the editorial system does not allow for it. However, just because a review says that the results of X and colleagues should be referenced does not mean that X or a colleague of X is a reviewer.
There are already good answers, but let me add a few thoughts on top.
My perspective as an editor for 10+ years and an editor-in-chief for 4 years is that editors are leaders in their community. With that comes the prestige, but also the responsibilities, and that includes communicating your expectations to authors and reviewers, as well as upholding the standards of your community. It isn't just about sending papers to reviewers, reviews back to authors, and hiding behind the reviewer ratings when making the call on a paper. It also includes sending papers back to authors without review when they are clearly not well written or simply not very interesting upon first reading. It also includes sending reviews back to reviewers if they are ethically questionable, or telling reviewers so if a review is just sloppy and unhelpful. In some cases, this may ruffle feathers; in the majority of cases it will earn you a reputation as an ethical person interested in upholding the reputation of science and the publishing process.
In your case, you will have to make a call whether you think that the request to cite a specific paper is justified. If it is, then everything is ok. If you think it isn't, you have the choice to either tell the authors to disregard the reviewer request, or to have a conversation with the reviewer about the request. If you do think that it is ethically questionable, then that is something you should let the reviewer know, and ask them to revise their review accordingly.
At the end of the day, if nobody ever calls out unethical behavior, we will have to become used to it. It is your role as a leader in the community to speak out if you think something is not right. I bet that in the long run, this will earn you more friends than enemies.
If the citation is relevant, it should be included. In this case, the editor need not do anything.
If the citation is not relevant, the editor should direct the authors to ignore the request.
In my experience, editors do not check the reviewers' recommendations.
I will add to the existing good answers with a heuristic that I use to distinguish appropriate and inappropriate requests for citation.
I always read the reviews before sending to the author, for a number of reasons, and when I see citations recommended, I apply a two-point test:
If a request for citations passes both tests, then it's generally valuable and legitimate feedback. If it fails them both, it's almost certainly not. In between, it's a judgement call.
If it's legitimate, I'll generally say nothing in the editorial comments. If it's dubious, I will try to gently make it clear that the comments are not mandatory, e.g., "The authors may wish to consider whether or not Reviewer 2's suggested citations are appropriate to include."
Finally, note that in some journals an editor can rate a reviewer, so if you find a person is giving poor reviews, you can convey that information to the other associate editors of a journal and make them think twice about asking the person to help.
It depends on the appropriateness but also on the phrasing. Is the inclusion of the reference stated as a condition for acceptance? Or is the reference more of a suggestion like "Hey, you miss this area of research - this reference is an example, but there are others and possible better ones!" Demanding to cite a paper (of a reviewer) is less often ok and I would carefully check this demand of a reviewer. I consider it more acceptable to politely point to a paper, but even that practice is debatable.
