It is, it's called a contract. Unfortunately too employers, like LU in this case, think they are to be ignored or altered at the EMPLOYERS whim. Partly because employees don't have the money to fight them.
And of course, if as an employee you decide you'll break the contract you get fired ...
I assume this thread - http://www.northstandchat.com/showthread.php?324061-Should-Tube-leaders-go-to-prison - wasn't a big enough binfest for you then ?
Yes it is, for what they CURRENTLY do. Now they are being asked to work extra unsocial hours. It's all very well saying 'I'd resign' if you have some two bit job that there is plenty of but there's hardly a huge amount of vacancies for tube drivers. Then again, why should you be forced to resign...
Which equates to just over a grand bribe once tax and NI is taken out and a measly £10 a week as a pay rise. I note YOU didn't comment on what YOU would do if your employer suddenly forced you to do a mixture of nights and days.