I may be wrong, but it couldn't have anything to do with ACA. There is no interaction between ACA and defined benefit or defined contribution plans (or at least none that I know of).
Not to say that there is no information ever requested for census purposes with respect to defined benefit or defined contribution employer costs, but I had never heard of any such need.
Is your client so difficult that they would not give you any information with respect to something they asked you to do for them? Not that it is easy to get to that point, but a good term for such a client is "ex-client".