Agreement is unenforceable because it restricts competition in an unreasonably large territory.
Agreement is unenforceable because it restricts competition for too long.
Agreement is unenforceable because it is boilerplate or ‘one size fits all’ and thus is not properly tailored to fairly address the situation.
Agreement is unenforceable because there is no or insufficient consideration (Employer has not provided employee anything of significant value in return for his NCA commitment)
Agreement is unenforceable because it allegedly arose out of the sale of a business or the assets of a business, but purchaser (new employer) did not properly protect its rights relating thereto. Closely related to this is whether proper assignments were executed if the original employer is not now the enforcing party.
Agreement is not enforceable because it does not fulfill a legitimate business purpose. The court will always look to the concept of whether there is a good business reasons for asking an employee to sign the agreement.  Common legitimate purposes may be to allow sufficient time to train new employees, to protect trade secrets and to protect customers or pricing information.
Agreement is not enforceable because it has not been properly updated or amended since its execution and circumstances underlying or law controlling may have changed.
Agreement is not enforceable because of certain choice of law provisions which dictate against the employer. NCAs generally have a provision establishing the which jurisdiction laws will govern the agreement.