You don't need to sign a contract. If you work you are affirming it by working. If you object to anything in the contract you must say so in writing otherwise you have accepted it.
Thugulike is right, you don't have to sign anything. In fact, you still have a contract even if nothing is ever written down. If someone says to you, "I'll pay you X to work for me and you say yes, you've got a contract. Of course, the details of the contract are open to argument...