Michaelia Cash released the decision yesterday citing "concerns ...that information about several witnesses could be leaked and investigations compromised" (from Labor blocked from seeing secret union volumes).
The ALP is predictably outraged and we will no doubt hear much more of this from ALP/Union acolytes. Behind the scenes, however, I am sure there is some understanding that this was a likely outcome.
I am still waiting for some sensible voices in the ALP/Unions to come out and react appropriately to the widespread corruption in Union ranks. It could start with distancing itself from the CFMEU, the Union most clearly tainted by widespread corruption.