Thanks for posting a clear message about this. The government has waffled all over the place on this over the past year or so. Frankly I had hoped they would put the hammer down and require passports for everything starting this year.
Although the requirement right now is only for air, folks need to realize that if they have to leave their cruise early and fly back to the U.S. - they then fall under the passport required rules. Princess
is even warning people of this.