I recently had a relaxing massage at the Golden Nu...

I recently had a relaxing massage at the Golden Nugget spa. Very nice, calm atmosphere inside the spa (which is isolated in one of the towers) with access to a sauna, steam room, and whirlpool. The cost was a bit more than I'd normally pay for a massage but I figured while on vacation it would be worthwhile to indulge a bit, and I did enjoy it. At the end of the service, I went to settle up and had the expected cost on a bill but was also informed I had to pay an additional gratuity at a fixed rate, though I had the option to add more. I do have a little bit of a problem with being forced into then giving a 20% gratuity on an already marked-up cost, and it was written into my bill at the end of the service without any prior indication thereof. I've doubled-checked my booking and had no indication when I showed up for my appointment. My service was great (and on a pure tipping for good service basis have no issue with the amount paid) but I should be allowed to tip according to my experience, or at least be informed in advance that this cost will be included.