What to do if a colleague is reviewing an unchanged paper that has been rejected before on my recommendation?
If you were asked to re-review an "unchanged" manuscript there are a number of things you can do (e.g., Asked again to review a paper, when the authors don't wish to modify it). The issue is that this is not the case. You are no longer part of the review process.
The first thing you should do is STOP. The behavior you have engaged in so far has been completely unethical and a clear violation of every reviewer agreement I have ever seen.
- Your colleague should never have told you about the paper under review.
- You should not have mention that you reviewed a similar paper in the past.
- Neither of you should have mentioned authors or the title.
- The actual manuscripts should never have been shared and/or compared
To a lesser extent, it is not even clear why you still have your copy of the manuscript.
The Committee on Publication Ethics (COPE) provides Ethical Guidelines for Peer Reviewers which can be thought of as best practice. These include:
respect the confidentiality of peer review and not reveal any details of a manuscript or its review, during or after the peer-review process, beyond those that are released by the journal
not involve anyone else in the review of a manuscript, including junior researchers they are mentoring, without first obtaining permission from the journal; the names of any individuals who have helped them with the review should be included with the returned review so that they are associated with the manuscript in the journal’s records and can also receive due credit for their efforts.
keep all manuscript and review details confidential.
Between the two reviewers, you've created quite a nasty situation. First -- the author did NOTHING wrong.
Second, you and your colleague have done something very wrong. The fact that you know nothing substantive has changed means you were essentially handed the manuscript, which is very bad behavior on both your parts.
My recommendation is that the new reviewer should probably contact the editor that sent him the manuscript and say simply "for reasons I choose not to discuss, I suddenly find myself in conflict, and can't provide a review", delete the paper, and never discuss it again. Your colleague is not in a situation where he should try to provide a fair review, as he's obviously poisoned.
The goal of the review process is to fairly and accurately evaluate the merits of the submitted manuscript, while making sure no one gains an unfair advantage through knowledge of the manuscript before it is available publicly.
I see no issue about unfair advantage here, since you and your colleague were both already in possession of the same manuscript. That being said, ethical boundaries are very field dependent, and the culture in your field may be different. For example, I have reviewed a number of papers and have never been explicitly asked to keep submitted manuscripts confidential (though it is generally understood that I should).
As for your colleague's responsibility of evaluating the paper, there is some unfortunate tension between the goals of fairness and accuracy, and you need to make a judgement based on the specifics of the situation. But here are the main points I think are important:
It is unreasonable to expect every reviewer to understand every tool used in a submitted paper. Discussion of papers (which both parties already have access to) is to be encouraged (though the fact that one is reviewing the paper being discussed should perhaps be kept confidential, depending on the situation). From this point of view, I would consider it unethical not to let your colleague know about a serious logical error in a paper they are reviewing.
On the other hand, your colleague should form their own critical opinion about the paper. Their knowledge that the paper was previously rejected and then resubmitted without any revision has (probably) already biased them against it.
So, if there is a serious issue in the paper which absolutely has to be pointed out, then by all means do so. Otherwise, I would do as the other answers suggest and let your colleague form their own opinion about it.
The fact that the authors have not addressed your original reasons for rejection is unsettling and could be a reflection of unethical behavior on their part, but without more information, we (and perhaps you) cannot know for sure.