Rule 48. Exemptive Relief — Extreme Market Volatility Condition
(a) In the event that extremely high market volatility is likely to have a Floor-wide impact on the ability of DMMs to arrange for the fair and orderly opening, reopening following a market-wide halt of trading at the Exchange, or closing of trading at the Exchange and that absent relief, the operation of the Exchange is likely to be impaired, a qualified Exchange officer may declare an extreme market volatility condition with respect to trading on or through the facilities of the Exchange.
(b) In the event that an extreme market volatility condition is declared with respect to trading on or through the facilities of the Exchange, a qualified Exchange officer shall be empowered to temporarily suspend at the opening of trading or reopening of trading following a market-wide trading halt: (i) the need for prior Floor Official or prior NYSE Floor operations approval to open or reopen a security at the Exchange (Rules 123D(1) and 79A.30); and/or (ii) applicable requirements to make pre-opening indications in a security (Rules 15 and 123D(1)).
The rest of the rule is here:
Not that this is happening or will happen, but something to understand in cases of market volatility.