How do you qualify a business with stock holders for credit union membership eligibility?

If you are a community-chartered credit union, then you will need to check your bylaws to ensure that they include businesses located within your geographic community.
NCUA has opined that federally-chartered credit unions that are not a community-chartered credit unions will need to ensure that all owners of the company, which includes stock holders, are within their field of membership. They don’t have to be members in their own right, just eligible for membership.
This can pose a challenge if the company is publicly traded. In those circumstances, the only available route may be to amend your charter to include the company itself as a Select Employee Group (SEG).
If you are a state-chartered credit union, you will need to look at how your individual state regulator has interpreted this issue. Also, keep in mind that membership eligibility is based on the ownership of the business at the time the account is opened and is not affected by future changes in ownership.
Once a member, always a member!