As an “at will” employee BOTH the employer and employee may terminate the employment relationship at any time, for any reason (or no reason). Employer’s termination cannot be for discriminatory reasons (i.e. race, age, gender, filing administrative complaint, etc.). If the employee initiates the break up he/she is free to work for any employer and use his/her knowledge and experience. However, oftentimes employees (especially sales, manager, executive) are bound by a non-compete agreement which can restrict an employee working in a competing industry to service specific customers and/or geography. Also some employers have their employees sign non-disclosure agreements to prohibit an ex-employee’s use of the company’s confidential and proprietary information (i.e. customer lists, pricing, formulas, etc.). Beware that employment law is a complex topic with many factors that will impact what an employee can and cannot do.
Disclaimer: The foregoing answer does not constitute legal advice, is provided for informational and educational purposes only for persons interested in the subject matter. Each situation is fact specific and may be subject to state specific laws. Without a comprehensive consultation and review of all the facts and documents at issue it is impossible to evaluate a legal problem fully. This answer does not create an attorney-client relationship.