Whenever two or more employers engaged in the same general line of business, employing in the aggregate not less than twenty-five persons, and having a common difference with their employees, shall, co-operating together, make application for arbitration, or whenever such application shall be made by the employees of two or more employers engaged in the same general line of business, such employees being not less than twenty-five in number, and having a common difference with their employers, or whenever the application shall be made jointly by the employers and employees in such case, the Department of Labor shall have the same powers and proceed in the same manner as if the application had been made by one employer, or by the employees of one employer, or by both.