I'm a PhD student at a university that is in the process of evaluating updates to stipend policies and one of the students involved in providing feedback on said policy updates. During a meeting a few weeks ago with the PIs in our department, our department's official policy on minimum student stipends and how they should be adjusted if the student wins a funding award was discussed. As a student with a large funding award I learned I should have been topped up by $5,000 above my original stipend amount, however, my supervisor had only topped me up by $500 annually. As my supervisor was in the meeting as well they are aware they have not been matching policy and acknowledged they need to fix things.
While my supervisor is trying to figure out how he can manage his lab budget to change things going forwards he hasn't said anything about making up for mistake of the last few years. I've had my award for 2.5 years now, meaning I'm effectively out $11,000 he should have been paying me all this time. I know lab grants are tricky and finding money for students in existing ones can be quite hard, but this should have been budgeted in if he had followed the policy properly.
How do I go about asking my supervisor if he is considering paying what are effectively back-wages from the past two years without ruining our relationship? It's been very good up until now and while I don't want to put a strain on it that money would really help me a lot financially.