Is that an Iranian sanction on the USA, or US law (hoping to make it easier to spot unwanted behaviour or something)?
It's Iran's requirement.[0]
[0]https://travel.state.gov/content/travel/en/international-tra...
[0]https://travel.state.gov/content/travel/en/international-tra...
Unlike the rest of the world, Americans can only visit with organized tours.[0]
[0]Unless you've got some Persian relatives you're visiting.