Defense Contractor - what happens if your clearance is denied

So I am working at a defense contractor (one of the big ones) and when I started working here I didn't have a clearance. I have an interim TS Clearance and my background check is ongoing. What happens if my clearance gets denied?

Will I be fired? Will they put me on only unclassified work? Or Any insight on how the defense contractors work would be greatly appreciated.