The Big House had plans to host both a Smash Bros. Melee and Smash Bros. Ultimate online event from Dec. 4th to 6th, 2020, but those plans have now been called off. The Big House took to their official Twitter account to reveal that Nintendo has sent a cease and desist for the event, forcing them to call off plans. Refunds for the event will be offered in the near future.
It seems Nintendo took issue with The Big House using Project Slippi to facilitate the online tournament. Project Slippi allows Smash Bros. Melee to automatically save replays, use live match mirroring, implements rollback netcode, and opens up online matchmaking. Obviously Nintendo isn't too keen on this sort of thing, hence the cease and desist.
Thanks to Andreslop24 for the heads up!
UPDATE - Nintendo has provided a statement on why they're stepping in to shut this tournament down. You can read it in full below.
Nintendo appreciates the love and dedication the fighting game community has for the Super Smash Bros. series. We have partnered with numerous Super Smash Bros. tournaments in the past and have hosted our own online and offline tournaments for the game, and we plan to continue that support in the future. Unfortunately, the upcoming Big House tournament announced plans to host an online tournament for Super Smash Bros. Melee that requires use of illegally copied versions of the game in conjunction with a mod called “Slippi” during their online event. Nintendo therefore contacted the tournament organizers to ask them to stop. They refused, leaving Nintendo no choice but to step in to protect its intellectual property and brands. Nintendo cannot condone or allow piracy of its intellectual property.