Many of Steve Earle's songs could be nominated.
Even stuff off 'The Revolution Starts Now' which only came out last year.
'Home To Houston' tells the story of a civilian truck driver in Iraq. It's a war song, a modern take perhaps, but a topic covered by much older folk songs than this and, alas, newer ones too probably.
ANother good candidate is 'Tom Ames' Prayer' as well as 'Valentine's Day'....oh, I could go on and on for ours.
'Harlan Man' is a Trade Union song about mining off the album 'The Mountain', the title track off that album was mentioned previously. Just about any track on that album coul have been folk because, as bluegrass, arguably it is already!