(1) In case any employee for whose injury or death compensation is payable under this chapter, shall, at the time of injury, be employed and paid jointly by two (2) or more employers subject to this chapter, the employers shall contribute to the payment of the compensation in a proportion of their several wage liability to the employee.
(2) If one (1) or more, but not all, of the employers are subject to this chapter, and otherwise subject to liability for compensation under this chapter, then the liability of those who are so subject shall be to pay the proportion of the entire compensation that their portion of the wage liability bears to the wages of the employee; provided, that nothing in this section shall prevent any agreement between the different employers between themselves as to the distribution of the ultimate burden of the compensation.