I am a final yr PhD student and my supervisor recently found out that I am planning to stay in science on do a post-doc. Since then, he has been making me do all kinds of random things that detract from finishing my thesis on time such as supervising undergrads for 12wk projects, training other PhD students from scratch etc. When I protest he tells me that he will have no problem recommending me for a job if I do these things he asks! Perhaps I'm over reacting but it does seem he is blackmailing me into doing these things because he knows I need to keep him on my side

How open is your relationship with him? If you are able to do so, I would ask him directly if he would give you a good reference even if you did not do these extra tasks. Then it is up to him to explain himself if he says "no".

I would say that a good supervisor would discourage a final year PhD student from all above activities not demands to do them. Sounds like a real blackmailing. Maybe you could calculate how much time you might devote to these activities so that your PhD still gets done in time and propose to your supervisor that you are doing this and that for so many hours.

I agree with Verdy. It sounds like a horrible situation to be in, but I think she is right. You should work out roughly how much time you are spending on the extras & go to your supervisor and express that you're concerned that it's detracting from the main task in hand at the moment i.e. finishing the thesis & you feel you are in a catch 22, because you want to do a good job. If the super is the manipulatitve type, try to work around it by appealing to their vanity & frame it as if you are actually asking for advice on how to handle things - whilst making it clear it's bothering you. hope it works out.

I agree that as a final year student finishing your thesis is a priority, but you also need to think about career development and in that sense the other stuff isnt entirely 'random'. If you want to do a post-doc you'll need other skills, and being able to say you have trained/supervised/managed other people will be good for CVs/applications.

Thank you so much for the usefull replies guys, some very helpful tips! Basically, my Boss is extremelly manipulative and will do/say pretty much anything to get you to do what he wants regardless of your best interests. Our lab is short of cash and so taking in more students will bring in extra money. I sent him a list of all the expts I need to do to in order to complete my thesis and it is huge! Hopefully he will now reconsider all these additional things without me having to refuse to take the students!