An advisory opinion from an appropriate labor organization is a requirement for the O-1 Visa (also known as the Artist Visa). Certain labor unions exist for the purposes of the O-1 petition, and these labor unions issue letters of no objection. In a nutshell, these letters state that the labor union does not object to the granting of the O-1 visa in your case. For O-1 purposes, it’s a letter to legitimize your professionalism within the field. For example, theatre performers usually secure letters from AGMA.
The advisory opinion is actually a technical requirement of the O-1 petition. If this letter is not included, USCIS may issue a Request for Further Evidence (RFE). It’s a letter to legitimize your professionalism within the field.
If there is no labor union for your profession, you need to include a peer consultation letter.
In conclusion, a requirement of the O-1 Visa is an advisory opinion from an appropriate labor union. If there’s no labor union assigned to your profession, you need to go to secure a letter from a peer organization, such as Fractured Atlas, which could be Fractured Atlas or a peer expert. The letter from the peer expert should contain information about your extraordinary ability and a description of your future work.