Based upon one of the letters sent by one of the law firms to Twitter[1] it seems that the arbitration agreement requires filing a separate individual arbitration agreement? "with each employee filing a separate individual agreement, as required by the terms of your arbitration agreement"?

It seems like Twitter's own arbitration terms is going to be the thing that hurts them here?

[1] https://twitter.com/AkivaMCohen/status/1598487532764798983/p...

If these were before a court then Twitter could try and have them combined into a class action suit. Twitter's contracts with these employees included arbitration clauses though. Normally companies prefer this because it heads off class action suits, but here Twitter has been hoist with his own petard. Twitter demanded the arbitration and now is paying the cost for that.

Here are some details of group, class and collective arbitration proceedings in the US https://www.nortonrosefulbright.com/en/knowledge/publication...

Bottom line is because arbitration is a bilateral process between the parties to a contract, both sides would need to agree to turn it into a collective arbitration. A class arbitration would be if one representative of the class took action on behalf of everyone (who didn't opt out) of that class.