The index committee is comprised of 10 members who are full-time employees of S&P Global, their identities other than 2 directors are kept secret. They meet once a month to discuss the potential revisions to the S&P 500 and votes by the index committee are decided by a simple majority.
“The Index Committee structure is intended to foster a collaborative decision-making process,” explained S&P. “All index committee members are encouraged to participate and voice their opinions and positions on all relevant matters. One role of any chairperson is to ensure everyone has their opportunity to opine on all decisions.”
https://qz.com/1587963/how-the-sp-500-is-built-and-who-decides-what-companies-go-in-it/