I have added two links to this answer which talk about at-will employment and non-compete agreements. First, you
Attorney's answer to this question is given for informational purposes only. Every factual situation is different and changes the application of the law to those facts. You should not rely on the answer as advice for your situation. By answering this question, no attorney-client relationship is intentional created, nor should one be implied. Before taking any actions, you should consult with an attorney to advice you on your specific situation.
I'm a Michigan licensed attorney. Since 2001, I've focused on employment law issues, including working with employers and employees to address noncompete issues.
I would certainly encourage you to check out the links provided by Mr. Dafoe as they are good resources. Additionally and going back to your question, your employer can't "force" you to sign a noncompete agreement. But your employer can condition your continued employment upon you signing a noncompete agreement, even if you have worked for the employer for a substantial amount of time. While for most employees such a situation really is not a fair choice, Michigan courts have found that continued employment without anything more is sufficient consideration to support a noncompete agreement. You may have potential defenses for why the noncompete agreement is not ultimately enforceable, those issues should be addressed with competent legal counsel, which I highly recommend before signing any agreement that may ultimately restrict or limit your future employment options. For information about enforceability issues, see the link I've provided.
Please go to www.shinnlegal.com for more information about my professional experience. But in sum, I'm licensed to practice law in Michigan. My response is provided only to educate the public about general issues that may need to be discussed with competent legal counsel in your state. My response is not a substitute for consulting an attorney in order to fully understand how the law may apply to your specific and unique circumstances; Remember, you often get what you pay for.
Talk to an attorney BEFORE you sign ANYTHING!!!
THIS ANSWER IS PURELY FOR ACADEMIC DISCUSSION ONLY AND DOES NOT CONSTITUTE ANY TYPE OF LEGAL ADVICE OR LEGAL REPRESENTATION.