World Bicycle Day is "a global day officially recognized by the United Nations to celebrate the power of bicycles".
Rides and events are planned through out the United States and World Bicycle Relief (a Chicago-based organization) will be in New York to celebrate with the United Nations.
Here's a little more information from their press release:
Global nonprofit and social enterprise, World Bicycle Relief, is joining the UN and the worldwide cycling community to celebrate the first-ever World Bicycle Day on Sunday, June 3, 2018. This designated annual day will promote bicycle use around the world and for World Bicycle Relief, helps showcase the positive impact a bicycle can create in the life of a person whose only option is walking. The organization provides specially-designed Buffalo Bicycles for people in developing countries where distance is a barrier to things like education, healthcare and entrepreneurial opportunities.
If you are looking for ways to be involved and learn more about Sunday's celebration, here is the full press release: