In US: must be an attorney licensed and in good standing in any state, territory or DC.
Outside US: must be a lawyer or equivalent (eg counselor, barrister, advocate, solicitor), duly educated and licensed/accredited and in good standing.
As a general rule, experienced and currently practicing lawyers, and those in the legal academy, are more likely to be admitted.
From Judge Alsup's Order re Motion to Compel Arbitration, Abernathy v. Door Dash (ND Cal. Feb. 10. 2020):
This case is addressed in the Redline query, Pro-provider arbitration clause for B2C online terms of service in the US.
For decades, the employer-side bar and their employer clients have forced arbitration clauses upon workers, thus taking away their right to go to court, and forced class-action waivers upon them too, thus taking away their ability to join collectively to vindicate common rights. The employer-side bar has succeeded in the United States Supreme Court to sustain such provisions. The irony, in this case, is that the workers wish to enforce the very provisions forced on them by seeking, even if by the thousands, individual arbitrations, the remnant of procedural rights left to them. The employer here, DoorDash, faced with having to actually honor its side of the bargain, now blanches at the cost of the filing fees it agreed to pay in the arbitration clause. No doubt, DoorDash never expected that so many would actually seek arbitration. Instead, in irony upon irony, DoorDash now wishes to resort to a class-wide lawsuit, the very device it denied to the workers, to avoid its duty to arbitrate. This hypocrisy will not be blessed, at least by this order.