I am seeking advice for the following situation: I finished my PhD in microbiology in September 2021, just before I submitted a paper to eLife with me being first author and my PhD advisor as corresponding author. The results of the first review round came in just after I left the lab and additional experiments were asked for by the reviewers. These were performed by another PhD student and resulted in two figures in the supplementary material and did not alter any of the conclusions of the paper. The additional experiments were performed using the exact same methodology and data analysis pipeline developed by me during three years. Merely the bacterial strain was different.
Yesterday I received the revised manuscript which states the other PhD student as co-first author with equal contribution (nobody informed me or asked for my opinion). I replied immediately to the PI that I cannot accept this, stating that an authorship is justified but certainly not an equal contribution. I hear from the lab that the other student's projects are not going well and that they are looking for a way to get her on a paper...
Now I am wondering if there is any chance that the revised paper could be accepted without my consent and what I should do if the PI refuses to "downgrade" the authorship of the other student. And should I also inform all other authors, that I don't agree with the author list?
EDIT April 14 I informed the PI that I did not agree on the order of the author list with respect to the authors' contributions and that I refused resubmission of the manuscript until I could seek further advice. The PI backed down and agreed on removing the "equal contribution" for the other student, not without trying to make me feel guilty.