If the 'legal company' is a law firm, they have no obligation to take your case. As mentioned, there is no discrimination against pot smokers. Depending on the circumstances, there could be discrimination against the disabled.
Discrimination means being targeted because of your race, age, gender, religion, national origin, etc., in an employment or housing context.
People in medical pot groups and disabled people aren't "protected classes," so they can be discriminated against in the workplace and in housing, and a "legal company" can refuse to provide services to them.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.