If it is a signed enforceable contract as you indicate, no, they cannot elect to pay you less than that--contracts are legally binding and can be enforced in court if necessary (i.e., you could sue if you had to for the money, based on the contract). Certainly, they can ask if you will agree to accept less (for example, if the company is having financial problems and it would help them), but is *your* choice whether to accept less than the amount to which you are contractually entitled.