Please help me diagnose my mechanical problem and if you know, please fill me in on what type of work needs to be done and what tools it will required.

My rear wheel has side to side movement, or "play" in it. I can kind of rattle it back and forth with my hand. The axle is snug in the dropouts and it doesn't move drastically, but kind of shakes back and forth when I move it with my hand. (I can manually rattle it a bit.)

I'm thinking something needs to be tightened or the bearings need to be worked on? Hubs are sealed cartridge bearings.

Thanks.