Samantha Bonizzi, a spokesperson for Equinox and SoulCycle, told CNN, "Neither Equinox nor SoulCycle have anything to do with the event later this week and do not support it.
She said she was adding the company to her list Wednesday morning and encouraged supporters to contact Related Companies.
After that, it will only be possible to be removed if Stephen Ross is no longer with Related Companies."
Though it's early in the campaign to boycott Equinox, the move could be a boon for competitors.
"Stephen Ross, owner of Equinox, SoulCycle, PURE Yoga, and Blink Fitness, is hosting a massive fundraiser in Southampton this weekend for Donald Trump.