Faction Rallies is a periodic event in Destiny 2 that actually went back into the workshop for quite a while following critical player feedback. Starting June 5 and running through June 12, Destiny 2 Faction Rallies return, and they’re quite a bit different from what you might remember.
The biggest change is that you can now only pledge to a single faction per account. This means no more loading up on New Monarchy, Dead Orbit, and Future War Cult across all three of your characters. As a player, you’ll have to pick one and commit for the week. You’ll be able to swap who you are pledged to for the next event, but each weekly event will limit you to one single faction. That might not seem like a huge deal, but the new rewards available make this decision a very meaningful choice. Vendors now have seasonal progression, much like the Vanguard or Iron Banner. Earning Faction Tokens and turning them in will increase this rank. Special Exotic armor ornaments are available by reaching a certain rank with each faction, and specific Exotic Masterwork weapon catalysts can be acquired by hitting rank fifty.

Dead Orbit will offer the Eye of Another World (Warlock) ornament and the Graviton Lance Catalyst
New Monarchy will offer the Crest of Alpha Lupi (Titan) ornament and the Sweet Business Catalyst
Future War Cult will offer the Knucklehead Radar (Hunter) ornament and the Sunshot Catalyst

If you want one of those specific rewards during this first Season 3 Faction ...