This has happened to me a couple of times, I have gone to work only to find out I am being floated. Then the unit I am floated to wants me to leave before 12 hours are up (the length of my usual shift), either because they don't have a full day's work for me (low census), or because the unit is outpatient and closing for the day (8 hour shifts there). When I complain to staffing they tell me there is nothing they can do and that I need to clock out and take vacation/holiday time or lose the rest of that day's pay. Can they do this, legally? People have also been floating twice and sometimes three times in one day at my hospital, which is a not very good alternative to being sent home since it is very stressful (floating once is bad enough!) If they don't have work for me, whatever, but I should be paid for the 12 hours, whether I go home or stay at work (I'd love a couple of free hours at work to read some nursing journals, actually).
If I was a salaried office worker here (and they never work uncompensated overtime, mind you), I'd be sitting around until 6:00 yammering on the phone or surfing the internet. They wouldn't send me home and dock my pay if there wasn't anything to do.