[serious] What is she entitled too ? (involves workplace hours etc.)

[thegreatone]

Hi all, i'm hoping you can shed some light on a law i heard quite some time back now in the UK, the right to refuse work ?
I've been googling madly for the past 2 hours or so, reading as much information as i can, and nowhere can i find it... I'm beginning to think its one big joke.

Well, say a contract is for 8 hours of work per week, and the person works those 8 hours without problems, is it then ok for that person to turn down additional hours offered to them by the same workplace ?

At the moment i have a friend (well, girlfriend) who is working alot and our spare time together is being ruined along with our plans because her workplace is forcing her to work more than her contract, when she trys to negotiate with them she is faced with disciplinary action...
I know this is wrong, but i cannot find the supporting law that should allow her to refuse additional hours at her will.

Can anyone shed some light on this ?
Please ?

Kudos and Rep. if you can...

EDIT: 16 year old woker here btw, i think this means she is entitled to study time off work..