[Update: I can't get the live streaming at this link above, but do have it by clicking here. If that doesn't work for you for some reason -- a friend said he couldn't get it -- it's also streaming here.]
The protesting performers are reported to include current and former Broadway cast members from such shows as Wicked, Beautiful, Hamilton, Phantom of the Opera, The King and I, Les Miserables, Cinderella, Xanadu, The Producers and Head Over Heels, as well as others.
A song list of some of the numbers they'll be performing as been published, but the one that most stands out to me is that they've asked people attending to bring along the song lyrics to "Do You Hear the People Sing?" from Les Miserables and join the cast.
As a warm-up, here's the number from the 25th anniversary concert -- with the lyrics, just in case...well, you want to later sing along...