Yes, you should be concerned--but there may be nothing you can do about it. Oral (spoken) promises, or even written promises not contained in a contract, are not enforcerable or binding. The only thing enforceable and binding in an employment law context is a written contract, so if you received a written contract, it's only what is in the contract that is enforceable--nothing else. However, because non-contractual assurances or promises are not enforceable, you can't make them give you what they told you that you would get--and they can terminat you if you don't sign the contract. You can try to negotiate, but be prepared that you may have no leverage and may have to choose between signing and losing your employment.