First and foremost, requiring COVID-19 vaccination in order to freely participate in an activity otherwise open to the public is clearly arbitrary discrimination against those who choose not to undergo this treatment. The Emergency Use Authorization under which such vaccines are distributed guarantees everyone choice to receive or not receive the vaccine. Those who are offered it must be told: “Should you decide not to receive it, it will not change your standard medical care.” Your organization is not above the FDA, or state, local or federal law when it comes to determining medical standards for the public.
Secondly, in the sense that being unvaccinated is a medical condition, or perceived as such (e.g. presumed infectiousness or likelihood to become debilitated) it violates civil rights statues of the United States (Americans with Disabilities Act) and California (Unruh Civil Rights Act), which both expressly equate being regarded as having a disability with actually having a disability. Thirdly, due to the high rate of COVID-19 vaccine refusal among several minority religious and ethnic communities, such a policy constitutes de facto religious and racial discrimination.
Make no mistake: having or not having had a COVID-19 vaccination is simply not a health or safety factor. The only justification for discriminating on such basis is that being vaccinated would protect others, and it does not. Taking any of the COVID-19 vaccines has never been shown to lower the risk of disease transmission. This is not just my opinion. This is the official position of the Food and Drug Administration, the only such organization in the United States authorized to issue such judgments.
The FDA Q&A for both vaccines approved to prevent COVID-19 in individuals says clearly that it is not known whether the vaccines will help protect against transmission at all.
Most vaccines that protect from viral illnesses also reduce transmission of the virus that causes the disease by those who are vaccinated. While it is hoped this will be the case, the scientific community does not yet know if [the COVID-19 vaccine] will reduce such transmission.
As for testing, all COVID-19 tests are Emergency Use Authorized only, which means unproven, and should not be used to discriminate due to the unknown nature of their results. If they are to be used for screening, FDA guidance is that it be used for all persons, regardless of preconceptions of who may test positive: https://www.fda.gov/medical-devices/coronavirus-covid-19-and-medical-devices/covid-19-test-uses-faqs-testing-sars-cov-2
Examples of screening include testing plans developed by a workplace to test all employees returning to the workplace regardless of exposure or signs and symptoms and testing plans developed by a school to test all students and faculty returning to the school regardless of exposure or signs and symptoms, with the intent of using those results to determine who may return or what protective measures to take on an individual basis.
It is not the prerogative of your organization to require of the public what must by law be optional. You stand nothing to gain by requiring vaccination of participants in any event, and only expose yourself to legal liability. Do the right thing and cancel all COVID-19 vaccination and testing requirements for your events now.