Yes, I've seen this many times over the years. Not always disclosed up front but always taken off when I complain. This is merely a bait-and-switch scheme so they can bump revenue and not show it in the room rate. Very popular with the low-end properties, but also being done in higher-end properties with things like a "resort fee" or the latest I saw was a "hotel service fee" and the only explanation was: every one else does it.

You might have trouble getting it reversed after leaving, but do pursue it. Maybe some time they will learn it's costing them more to reverse the charge than what they are making.