Conn. Gen. Stat. § 31-328: Mutual associations authorized.

With the approval of the Insurance Commissioner, employers who are subject to this chapter and are bound to pay compensation to their employees thereunder may associate themselves, in accordance with the law for the formation of corporations without capital stock, for the purpose of establishing and maintaining mutual associations to insure their liabilities under this chapter; but no such association shall be formed to include employers not in the same or similar trade or business or in trades or businesses with substantially similar degrees of hazard of injury to employees.