more than 500 employees shall participate in the System with respect to all newly hired employees and employees with expiring temporary employment authorization documents. (F) Agricultural employment Not later than 4 years after regulations are published implementing this subsection, employers of employees performing agricultural employment shall participate in the System with respect to all newly hired employees and employees with expiring temporary employment authorization documents. An agricultural employee shall not be counted for purposes of subparagraph (D) or (E). (G) All employers Except as provided in subparagraph (H), not later than 4 years after regulations are published implementing this subsection, all employers shall participate in the System with respect to all newly hired employees and employees with expiring temporary employment authorization documents. (H) Tribal government employers (i) Rulemaking In developing regulations to implement this subsection, the Secretary shall— (I) consider the effects of this section on federally recognized Indian tribes and tribal members