An agreement between 2 or more shareholders, if in writing and signed by the parties, may provide that in exercising voting rights, the shares held by them shall be voted as provided in the agreement, or as they may agree, or as determined in accordance with a procedure agreed upon by them. A voting agreement executed pursuant to this section, whether or not proxies are executed pursuant to the agreement, is not subject to sections 466 through 468. A voting agreement under this section shall be specifically enforceable.