Iowa Code § 489.1111
A member of a professional limited liability company shall not create or enter into a voting trust or any other agreement conferring upon any other person the right to vote or otherwise represent any interests of a professional limited liability company, and no such voting trust or agreement is valid or effective. Any proxy of a member of a professional limited liability company shall be an individual licensed to practice a profession in this state which the professional limited liability company is authorized to practice. Any provision in any proxy instrument denying the right of the member to revoke the proxy at any time or for any period of time is not valid or effective. This section does not otherwise limit the right of a member to vote by proxy, but the certificate of organization or operating agreement of the professional limited liability company may further limit or deny the right to vote by proxy.
Iowa Code § 489.1111