The operations were purchased and closed down by Massey Energy at a bankruptcy sale in August. Shutting down the mines essentially stopped health care benefits, collective bargaining and job rights of about 5,000 of Horizon's employees and retirees.
United Mine Workers of America members have demonstrated throughout Horizon’s bankruptcy case.
Massey has said it will consider hiring Horizon's former employees if they are not union members.
"We are open to hiring any and all experienced miners. But we are not a union operation; it's all up to those miners," Massey spokeswoman Katharine Kenny told Associated Press earlier this month.