my employer has breached my terms of contract?

they have made changes to my contract without informing me in writing or me agreeing to it. as a result i am now worse off in terms of wages. the citizens advice have reccomended i initiate the company grievience procedure then onto tribunal for unlawful deduction of wages if i get no joy.. i have never been in this posistion before is this the right thing to do?i work in the uk