At the start of "When I Die, I Want Your Hands on My Eyes," which is the sixth episode of Mayans M.C. Season 4, the club gets word about the attack on Oakland during a ceremony honoring the dead.
Initially, they're unsure about just who perpetrated the attack, but Hank soon learns Oakland was able to positively identified the Sons of Anarchy as its attackers.
This gave Terry, who already wanted to attack the Mayans for a territory breach, the backing he needed from the rest of the Sons of Anarchy to attack the rival biker organization.