Enforcement is underway for Mayor Bill de Blasio administration's Key to NYC Program. The mayor says it's another way to encourage people to get the vaccine.

If you haven't gotten the shot yet, that means no indoor dining, movie-watching or visiting a gym. De Blasio says it will make customers feel safer knowing they are around others who are also vaccinated.

MORE: Find out how to show proof of vaccination 

The program started back on Aug. 17. As of today, it is being enforced with the city making sure businesses comply or face fines.

Those 12 and older who can get vaccinated must now show proof that they received at least one dose before they can access indoor dining at restaurants and bars, entertainment venues like museums, zoos and aquariums. This also includes fitness centers and gyms. De Blasio says there's been a good response from businesses and he's eager to see it take effect.

The mayor adds that mandates and other incentives will continue to be offered to sway those who have not been vaccinated.