US Affiliate Marketers - Licenses?

I have seen a couple of sources say that US affiliate marketers need a business license. Is this true? Do you have a license? Is there a certain amount of income from affiliate marketing that one would need to reach before needing to attain a business license?

I would say some people already doing that like some sort of sole proprietor or limited liability company or something like that anyway. Can we really do anything with that or not ? I do hope it will really make wonders with that. Can we do anything ? I am not able to give direct answer.