Editor's note: Inc.com columnist Alison Green answers questions about workplace and management issues -- everything from how to deal with a micromanaging boss to how to talk to someone on your team about body odor.

A reader writes:

I work on a team of three (plus our manager) as a supporting associate for two salespeople. I like my role and have no problem doing what other people might view as menial tasks, such as data entry and filling out form letters, in order to free up the salespeople's time so they can focus on their clients. I knew that was a lot of what the job entailed when I signed on and I willingly accepted.

One of the salespeople is a more recent addition to the team. In the last few months, he has taken to doing parts of my job himself. He did ask me to show him how to do some of these tasks and I gladly agreed, but at the time it was framed in more of an informational way or so he could cover those responsibilities if I'm out of the office. Now I find him doing them a few times a week while I'm here -- writing letters I should be writing, responding to emails I should be answering, and so on. I don't get the sense that he does it because he has problems with the quality of my work, but because he views it as a favor to me to do some of these tasks on his own.

I appreciate that he might feel bad that I get stuck doing some rather dull work, but it is why I'm here and what I'm getting paid to do, and I genuinely don't mind it. In the past when we've been extremely busy, he would constantly apologize for the amount of work he was giving me, and I would always reply with "That's what I'm here for!" or "Well, that's my job!" in a sincere and friendly tone. I really don't know what triggered his deciding to take on my work for himself because I can't imagine that I've given off the impression that I am overwhelmed or annoyed by my responsibilities. Frankly, what does annoy me is that he spends his time doing my job when I think that time could be better spent focusing on his sales -- especially since I receive a monthly bonus based in part on his performance.

I have experience dealing with slackers who aren't doing enough work and have no problem with those conversations, but asking someone to actually do less work is a new one for me. How do I get him to stop doing this without seeming ungrateful or rude?

This might be the perfect time for the "I've noticed you're doing X, and I'm wondering if I've caused that in some way" model. This model is useful in situations where something isn't sitting quite right with you, but you want to start by checking whether you might have inadvertently contributed to it. (For example: "I've noticed that you've been sending all my work through Bob to be checked, when you didn't used to, and I'm wondering if something has happened on my end that made you feel you needed to.") This is often a good approach to take because (a) sometimes you did cause the thing that's now worrying you, and it's useful to find that out, (b) raising it this way is a lot more polite than assuming that you didn't contribute in some way, and (c) you end up sounding like someone open to feedback, which is always a good thing.

In your case, it could sound like this: ''I've noticed you're doing X, Y, and Z yourself. I normally do those tasks for the other salespeople, and I'm wondering if I've given you the impression that it's an imposition for me to take this work for you or if I've handled any of it differently than you would have liked."

If he assures you that no, he just prefers to do this stuff himself, then your next move really comes down to whether or not it's his prerogative to make this call. If it is, then you could say, "I'm happier when I'm busy, and I'm here to do this stuff, so my preference is to handle this stuff, unless you strongly prefer to do it yourself. And of course, if you have preferences about how it's done, I'd be glad to do it the way you want."

But if it's not entirely his prerogative -- it it's eventually going to turn into a problem (if, for instance, your manager concludes at some point that your time -- and/or his -- isn't being spent well) -- then you need to be straightforward about that. In that case, you could say something like, "My sense is that Boss does want to funnel this stuff to me, but I hear you that you prefer to handle it on your own. Let me talk with her about what would make sense -- I just want to make sure she's in the loop since it's a change in the systems we've used so far."

Note: You don't to say this with a tone that implies "the boss will overrule you on this when she hears about it," because she very well might not. She might be totally fine with this guy handling this stuff. So your tone should be neutral and helpful, not annoyed or implying "this will not stand!"

As so often is the case, this is mostly about being straightforward but finding non-weird, non-accusatory language to do that with.

Want to submit a question of your own? Send it to alison@askamanager.org.