its Merle Travis' Sixteen Tons, they do not have a link to the spot so apparently they could not find it online as they usualy do when its availible. The spot is aparently called 'Model Miners'

It takes some big brass ones to pitch propiganda like that... lets have models sing about how much a coal miners life stinks to promote our coal... how do you pitch that??

Cool song though and the spot works... Talk about counter-intuitive advertising.