Membership is limited to those persons including: Employees of Atmos and its subsidiaries. Any business or organization whose employees or members are within this field of membership. Persons who are receiving retirement, pension, or other benefits as a result of prior employment by any such business or organization. Spouses of persons who died while within the field of membership of this credit union Groups of employees or members of companies or associations which are located within ten miles of this credit union's main office or an additional office and which have furnished written evidence of sponsor support to the credit union; provided however, that (1) any group having more than 300 employees or 500 members or (2) any group already being served as primary members of another credit union shall be admitted only by an amendment of this section which specifically names the group being admitted.