When The Dominators attack Earth next week during Invasion they'll be taking on none other than the Justice League, or at least the DC TV version of Justice League made up of Arrow, The Flash, Supergirl and DC's Legends of Tomorrow.
An eagle-eyed redditor pointed out that The CW Invasion posters feature the Justice League Hall of Justice in the background. When the posters are put together side-by-side, such as in the following promo pic below, the Justice League Hall of Justice can clearly be seen.
Update: The Hall Of Justice is Star Labs as revealed in the Invasion Flash crossover episode.
While TV DC TV characters are separate from the movie universe, the Justice League founding members do exist within the Arrow-verse. We've already seen The Flash, Martian Manhunter and Superman; there has been reference to Batman a couple of times (most recently on Supergirl), and Hal Jordan Green Lantern has been referenced on The Flash, which leaves Wonder Woman and Aquaman. To be clear, this doesn't mean we'll get to see the founding Justice League characters on TV, just that the shows give an obvious nod to the characters.
It very well could be possible that as a result of the Dominators attacking Earth that the characters on Supergirl, Arrow, The Flash and DC's Legends of Tomorrow decide to form their own group, much like the Justice Society before them. Maybe if Zack Snyder has no plans to use the Hall of Justice (too popcorn-y for Snyder), WB will let the DC TV universe use the Hall of Justice for the Arrow-verse. Snyder might opt to use the satellite version of the Justice League headquarters, aka the Watchtower.
Executive producer Andrew Kreiseberg also based their Tyler Hoechlin Superman in part on the classic version, as seen in the Superfiends animated series, which features the Hall of Justice, so this is another cool Easter Egg to the show. The Legion of Doom is also coming to DC's Legends of Tomorrow.
The Hall of Justice also resembles the Cincinnati Museum Center at Union Terminal in real life.
The CW DC "Invasion" crossover begins Monday, November 28th at 8pm ET with Supergirl on The CW.