Common practice in Worm, where both superheroes and rivaling super-villains will gang up on anyone causing enough trouble or breaking the unwritten rules, such as attacking a cape's family.
"Word gets around, and the cape community goes after the fucker. Protecting the status quo, keeping the game afloat. Bitter enemies call a truce, everyone bands together, favors get called in and everyone does their damndest to put the asshole down."
And when Endbringers attack, virtually every parahuman available will come together.
"This is why we are tolerated, why society allows and accounts for the capes that walk the streets and fight in its towns. Because we are needed for situations like this."
In Cult of Personality, the oWn is trying to wipe out the RED and BLU corperations, and a band of mercenaries from both sides have to fight together to push oWn back.
In May Xnocens July and Borne are only enemies because of the questionable things July does to keep Idius March from being released. Once Idius March is released this becomes a moot point and they team up.
In Chrono Hustle Jack is running around the timeline, and Melinda has been assigned to capture him, but Jack doesn't want to be locked up, since they can't send him back to his own time. But then it turns out that there's some big conspiracy going on, and they end up working together.
When Whateley Academy is attacked by a massive invading army, the usually bickering students drop everything to drive them off (though some of the Ultraviolents kept a few for the sake of... entertainment).
A key part of the Whateley Charter is that anyone, charter signatory or otherwise, who attacks any student's family as a way of getting to said student is to be treated as fair game by the signatories for anything up to and including orbital bombardment. Generally, those who have tried this in the past didn't survive long - this is one situation where the superheroes won't even try to restraint the supervillains.