No, you are incorrect: the employer may make you sign an employee agreement at *any* time. Until and unless you have an employment contract protecting or guarantying your employment in some way (i.e. restricting or limiting the employer's ability to fire you, or gurantying you employment for a certain period or time), you are an employee at will. An employee at will may be terminated at any time, for any reason whatsover. Among other things, that means that the employer can tell you to sign an agreement and, if you don't, terminate you for not doing so. And if you do sign, your continued employment constitutes sufficient "consideration" to make the agreement binding and enforceable. So yes--you will have to sign.