Batman has never been much of a team player, so it may not come as much of a surprise that he quits the Justice League along with several other heroes, in the first episode of Young Justice: Outsiders. When the Justice League appears to no longer be able to function autonomously as it needs to combat metahuman child abduction and trafficking, Batman says a new team is needed, one outside the purview of the UN and Secretary General Lex Luthor.
While the decision seems abrupt after a mission gone bad, it was actually a coordinated effort and planned ahead of time with Green Arrow and a few other heroes. Batman thinks this new team can do things the Justice League won't, walking out of a Justice League meeting and urging other heroes to follow him. While some are reluctant to join, and there may be more to come, Justice League loses 11 members including with Batman.
This one's a no-brainer. Believing Lex Luthor, who is now Secretary General of the UN, is working behind the scenes to turn countries against the Justice League, Batman suggests the League has "outlived its usefulness on Earth." While the League stands as an important symbol, but "all that matters is the mission. And if the UN's a roadblock to that mission, then we remove it. By removing the League."
He tenders his resignation on the spot, inspiring others to do the same, although he's the only founding member to quit so far. He'll presumably establish the Outsiders as he does in the comics and conduct missions the League can't.
Like Batman, Green Arrow has never been so hot on being a team player. Oliver Queen resigns immediately after Bruce, much to the chagrin of Black Canary. He urges her join, but she refuses furious with him for blindsiding the rest of the League and taking part in Batman's theatrics.
Plastic Man doesn't attend the meeting in person, but his hologram immediately gets stamped with a "design" stamp as he wordlessly signs off following Green Arrow's resignation.
Katana, also attending via hologram, resigns and signs off along with Plastic Man and several others immediately following Batman and Green Arrow's departure.
Making his Young Justice debut, although not for long, is Hardware, the high-tech equipped superhero. He's also appearing as a hologram and signs off, resigning with the others.
Understandably siding with Batman, Batwoman also wordlessly ends her hologram attendance as she resigns along with Plastic Man, Katana, and Hardware.
Nightwing technically already took a leave of absence from the League before Batman's little coup, but given the fact that he's running missions the League wouldn't approve of, without any branded logos, he'll likely end up joining Batman and would have departed alongside his former mentor if he was present at the time.
He's not a part of Batman's departure either, but feeling guilt over accidentally killing a child turned metahuman monster and temporarily losing his powers, Jefferson Pierce departs the League intending to also leave the life of being a superhero behind. He vehemently tells Batman he has no desire "Batman Incorporated," but he may not stay out of the action forever.
Robin (Tim Drake)
While the former Titans' official roles in the Justice League isn't clear (they all have "B" designations), they have always functioned as an offshoot of the League anyway, so the ones that leave with their mentors can also be considered official resignations. And, of course, Robin leaves with Batman.
Following suit with many other Bat Family members, Spoiler, AKA Stephanie Brown, follows Batman and Robin when they walk out of the Watchtower.
Green Arrow's newest sidekick, Arrowette, AKA Cissie King-Jones, follows Oliver Queen when he walks out of the Watchtower