This actually makes you an ideal contractor, you just have to know how to do this tactfully.
The real issue with this situation is working as a contractor on a single project. At the point you're working for one client, full time, as a contractor...you're an employee.
If you've got no other clients, you have no ability to negotiate with the simple statement, "I have other clients I have to tend to and can't dedicate time to this work until the contract is addressed. Let me know when you're ready to resume."