The Federal Trade Commission wants you to be aware that websites earn money when you click on their links. Its a perfectly reasonable law, to make sure you are aware that some links will result in financial compensation for the person who posted the link.
HoustonPhotowalks uses affiliate marketing to generate revenue for our budget and the organizers who run the group. This money is used to pay Meetup.com fees, website hosting fees, classroom fees, teaching fees, donations to museums and venues, provide bottles of water when possible, etc.