I'm traveling the west coast this week and about to go completely offline in Mexico, but the internet's been buzzing about all this this morning. Instead of reading a lot of bad reporting, I think it's best to see what IOSHA actually said. In this video, Indiana Department of Labor Commissioner Lori A. Torres talks about the fines and details (if the video is not embedding correctly you can see it here):
A second video introduces the report but apparently I can only embed one video on this page, so follow this link to see it.
Updated: Full video with better audio here.
On a VERY cursory listen/read, the initial media reports of the union being "blamed for the collapse" do not seem to be fully correct--they were cited for inadequate fall protection, etc. IOSHA fined the state fair commission for not handling the weather issues better (correctly, in my opinion), and as for the structure they fined Mid-America Sound for not following the PLASA standard "ANSI E1.21 - 2006, Temporary Ground-Supported Overhead Structures Used To Cover Stage Areas and Support Equipment in the Production of Outdoor Entertainment Events". They also apparently talked to James Thomas Engineering (the manufacturer of the roof) but didn't cite them, but since they are based in Texas (see Derek's comment below) I they may not have any jurisdiction.
Apparently, the main structural report by Thornton Tomasetti has not been issued yet, nor has the DeWitt (safety) report.
My series of rants on this issue from August start here.