I'll ask but I don't think there is anything 'official' on this because I know of a handful of folks who actually have been MOB'd from the IRR and I don't think the Navy wants to limit itself to who it can MOB anyways. That said you are pretty certain not to get MOB'd in the IRR, the very few folks who I know of being MOB'd from the IRR in the Navy had specialized skills, were MOB'd for specific billets and weren't URL's.
I would also ask your NOSC, if they were halfway competent they would be able to find the reference but since many NOSC's aren't halfway competent....
Being
involuntarily mobilized out of the IRR (there are two IRR flavors: the VTU and the ASP) is next to impossible unless we have another emergency and there are not enough people in SELRES to support. Someone correct me please if this is inaccurate. The last time I heard of people being involuntarily mobilized out of the IRR was back in 2009. Out of curiosity, I will do some research on this.
When I asked a ADMINO from one of the NOSCs about the VTU, his immediate response was, "you know you can still get mobilized from the VTU?" I think there is negative sentiment about the VTU because the NOSC CO is the reporting senior for the VTU unless otherwise delegated. The VTU is there for a reason and if the NOSC naysayers do not like it then they need to sack up and ask
CNRFC actual to remove it. Otherwise they need to stuff it and do their jobs as NOSC CO's and support the VTU like any other Reserve unit.
People in the VTU IRR, however, can
volunteer to mobilization or go on other orders types (ADT, ADSW, etc.). You will hear certain turds at the NOSCs telling you otherwise, which is referenced in RESPERS M-1001.5, so always ask for them to cite the applicable reference when they tell you anything.