Employee Stock Ownership Association と訳すのが正確です。
例:
I have joined my company's employee stock ownership association.
私は会社の従業員持株会に入っています。
Please contact the administration office of the stock ownership association.
持株会事務局に問い合わせてください。
employee stock ownership association = 従業員持株会
administration office / secretariat = 事務局