Because of the migrant crisis, Austria and several other countries around had (more) random checks at borders and other points inside the country for a while now (well "random" ... sometimes for days or weeks at the same place) .
And indeed, now it was announced that it apparently isn't going to be just random anymore (but not much details are known yet, sadly). This should be only temporary (hopefully), but a specific end date is not known currently. If you come to Autria before Friday, chances are that nothing changed until then. Currently (18.Jan.2016) it's only planned, but not yet in action.
Who may enter/leave should not change, but now a passport (etc.) will be required even for Schengen members. Strictly speaking, an ID was required before too, but most people were not checked at all during their stay in Austria. Now, it's necessary to come in in the first place.
(I'm not a lawyer.)