Authorship when PhD project given to new post-doc? I'm in the mid stages of my PhD, working on 3/4 of the components of a major project in our group. A post-doc has just started working on the remaining 1/4 using protocols I established (to keep our work comparable). My supervisor has now reassigned a lot of my original work to the post-doc, and let them re-optimise protocols independently. 

Now it's looking like I will have no authorship for the majority of the project, as the post-doc modified my protocols (which were meant to be consistent between us) and has taken over the bulk of my project.

What can I do to ensure I still get first-author publications out of my PhD? I have spoken with my supervisor who does not want to discuss authorship 'at this stage' and has been known to publish in the past without consulting other members of the group.

Thanks
First things first: I fully agree with Buffy and whoever else that this sounds like a very dodgy situation. A supervisor reassigning work and then 'not wanting to discuss authorship at this stage' takes an enormous amount of agency away from you as a PhD student. That has to be demotivating and frustrating. You could indeed look into transferring to another supervisor.

If you want to stay with this group, the project sounds like a co-first authorship to me. If you've done 3/4 of the project already, that seems fair even if the postdoc will optimise some of your results. Since taking it up with your supervisor wasn't really fruitful, talk to the postdoc and make sure they see this project as a shared first publication as well. After that, stay involved by discussing results, , asking what you can do to help, helping with troubleshooting etc. Make sure you know what stage the project is at and especially when writing starts, help with that. Obviously if you can improve on results, that's a bonus, but just staying involved should come a long way.