A provision in any written contract to settle by arbitration a controversy thereafter arising out of such contract, or an agreement in writing to submit to arbitration any controversy existing at the time of the agreement to submit, shall be valid, irrevocable, and enforceable, save upon such grounds as exist at law or in equity for the revocation of any contract. The provisions of this chapter shall not apply to any arbitration agreement between employers and employees, or between employers and associations of employees unless such agreement specifically provides that it shall be subject to the provisions of this chapter.