The Adjudicator's Field Manual states that "consultations are advisory in nature only and are not binding on USCIS. A negative consultation does not automatically result in the denial of the petition, as decisions must be based on the totality of the evidence. Accordingly, if the petitioner can submit evidence that overcomes a negative advisory opinion and which establishes the merits of the alien, USCIS may approve the petition." However, it is good to note that USCIS does take the content of the consultations seriously. Negative consultations have been a basis for denials in the past. If you get a negative consultation, please contact an immigration attorney immediately to help you proceed.
Sometimes your field of endeavor just does not have a relevant peer group or union. Maybe your art form is too cutting-edge for there to be an appropriate management group. In those cases what do you do? USCIS states that "If the petitioner can demonstrate that an appropriate peer group, including a labor organization, does not exist the decision will be based on the evidence of record."
All labor unions and peer groups are not the same. In fact, they tend to differ greatly when it comes to providing consultation letters. For example Actor's Equity and the Director's Guild of America are notorious for giving out bad consultation letters. For a complete list of appropriate peer groups and labor organizations please go here.
Every single peer group and labor union will have varying requirements as to what to submit when applying for a consultation letter. Some will want the minimum, in order to avoid wading through piles of paperwork, and some will want everything you submit to USCIS. Every organization will also have greatly differing fees. It is advisable to consult with each organization directly in order to figure out what exactly they want.
A consultation may be waived for an alien with extraordinary ability in the field of arts if the alien seeks readmission to perform similar services within 2 years of the date of a previous consultation. Petitioners should submit a waiver request and a copy of the previous consultation with the petition.
For more information about the O1 / Artist visa check out our O1 / Artist Visa Application Guide and O1 / Artist Visa Immigration FAQ.