Yes, you do need to bring your passport on any of our tours into Mexico.
Historically, going into Mexico has not required a passport. However, recent law now states that a passport is required to enter into Mexico or to get back into the United States! It is required that you bring your passport on the trip in case immigration officers on either side of the border asks for it. As they say, "Better to bring it and not need it , than to need it and not have it!!!" If you decide to come on the trip without a passport and you are not allowed to go into Mexico, then you will have to stay behind and find a return trip back home on your own without any refund for the tour.