The requirement will first be implemented in New York City, but the company said it "plans to introduce similar policies in all of its markets and will continue to follow all current local health guidelines."
Equinox, known for high-end amenities such as eucalyptus steam rooms, operates 23 gyms in Southern California.
SoulCycle, which focuses on indoor cycling and spinning classes, lists 11 locations in SoCal.
The policies were supposed to take effect by early September in New York. A timeline was not offered on when they would roll out the requirements to other regions like Southern California.
"We have always made the health and safety of our communities our top priority, and we will continue to do so in partnership with infectious disease experts as well as local governments," said Harvey Spevak, Equinox Group executive chairman and managing partner. "We have a responsibility to take bold action and respond to changing circumstances with urgency. We encourage other leading brands to join us in this effort to best protect our communities."
The decision comes as more private and public employers, including Disney, Kaiser Permanente, Google and Microsoft, have been requiring employees to be vaccinated.
Some bars and restaurants in Southern California are also asking customers to show proof of vaccination or negative COVID-19 test to be served.
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COVID-19 cases throughout the country have been surging this summer as the highly-contagious delta variant takes hold among the unvaccinated.