E-World Tours Optional spots become compulsory without notice New York City New York

It is a terrible experience.

On the third day of the tour, which was a day-tour in New York City. There were 3 optional admissions/tours for us, as I have already been to those places, I decided not to join any of those optional tours nor admissions.

Whenever we went to an optional admission spot, I told the tour guide, Frank, I would not join this one and the tour guide acknowledged it. And I do it again for the second and third optional admission. However, when I spoke to Frank at the third optional spot, he said "OK, but you have to pay a penalty for USD$35." I wonder why but he refused to explan and just asked me to make a dial to the travel agency if I have any doubts.

When I called to the travel agency, they admited that there is a special rule that if any customer do not join any optional tours, he/she has to pay a penalty for USD$35. HOWEVER, I cannot find any policy or terms & conditions regarding to the penalty both on my receipt nor their phamlets. The company explained that it is a hidden rule and assume every customer joining their tour would know this. I think it is ridiculous and unreasonable. If I have to pay a penalty fee, would it be an "OPTIONAL" tour?

I am not sure about any legal issues in US but in my hometown Hong Kong, I am quite sure the penalty and the "hidden rule" could not be a valid term&condition as the customer has never been told or acknowledged about this rule before the contract is signed, not to mention that the tour guide, Frank, did not say anything about it until I told him I would not join the third optional tour.

If I was told before the tour start, or at the very beginning, I could have had time to consider which optional tour I would join if it is really "COMPULSORY" but not optional. I am really disappointed to this ridiculous Chinese tour agency. I do think there should be some legal regulations for those terms and conditions in order to prevent any tourists suffering losts like me.