A vessel engaged in the coastwise transportation of coal produced in the United States, from a port in the United States to another port in the United States, shall be given priority in loading at any of those ports ahead of a waiting vessel engaged in the export transportation of coal produced in the United States. However, if the Secretary of Transportation finds that it is in the national interest, the Secretary may eliminate this priority loading at any port. The Secretary shall report to Congress within 30 days an action eliminating priority loading under this section.