Floating Dilemna

Is it fair to float in other areas if you were hired to work only in a specific medical unit? The contract that my best friend signed specifically stated that she will only work in a specific medical unit.But when she started working,her manager told her that after three months she will float in areas such as cardiovascular,surgical,neurology,oncology and ortho which are not part of the unit that she's working in right now..Can she say no? I actually am fortunate because I don't get to float in the hospital where I'm working in.She ask me once about this and since I don't have any idea I opted to open this up here in our allnurses forum. Thanks in advance for your future inputs!