Air Traffic Control System Command Center Advisory 23 by the Traffic Management Command Center (DCC) at date [..] - all united airlines ... ground stop.

Here is about ground stops: https://www.faa.gov/air_traffic/publications/atpubs/foa_html...

My understanding is that applies to United Airlines and it’s regional partners. It seems each airline is making their own decision.

This Reddit post seems to have more info: https://old.reddit.com/r/flying/comments/108yjgz/faa_notams_...

Reads United Airlines apparently.