Research partner switching authorship before publishing to Arxiv? We’re currently publishing a preview of a paper we’ve just gotten accepted to a conference and of the five of us, one member started an Arxiv submission application first. This means that the rest of us were not able to submit an application in lieu of his, even though he did not have the final version of the paper. In submitting the work to Arxiv, he actually switched the originally alphabetical authorship so that his name went first.

How can you force someone to remove their submission? We keep texting him, but he is ignoring us, and if this continues, this falsely authored version will be what is published and out there, but different from the legitimate version of the paper.
Make sure this is actually malicious.  If so Contact arXiv.

For co-authored papers every author should be an owner of the paper. Usually, the person who submitted the paper gives the other authors the password. It sounds like that will be problematic in this case, but you can claim ownership of your paper without the password through the arXiv system.  (This will require manual intervention from someone at arXiv.)

On the contact form there you should probably explain exactly the situation.  They are going to be the only ones who can properly address and sort through what is going on.

Needless to say, you should make absolutely sure that this rogue coauthor is intending to do this and it is not some sort of mistake.  It seems like extremely odd behavior since the paper is already submitted with the correct authorship, so it's quite easy to prove he has changed the order.  Also, once you bring this to the arXiv's attention it could have consequences for this coauthor, such as getting banned from submitting papers, etc, so make sure the act really is malicious before doing this.