An employee under the terms of employment with the company's "At-will" policy is not under a contract with the company. An at-will employee can be "fired" at any time for almost any reason; although employees also have the similar right to quit the job at any time without further notice to the employer.
How to Determine if "At-Will" is Appropriate for Appointment Letters
How do you know "AT-WILL" is the best term to fit into the appointment letter without knowing the basic rights of such an employee?
Lay-off for At-Will Employees
Though the employer has unmitigated rights to sack/fire the employee, the lay-off falls under the minimum requisition of notice period to the employee only in case of (i) no bias towards race, caste, creed, sex, marital status, religion, and country-specific reasons.
Employee Right to At-Will Termination
Here, the employee termination policy has to be different, stating that firing should be done only in case of performance or behavioral aspects and not due to unnecessary causes.
Most importantly, employers have new employees sign a form stating that they are being hired on an "at-will" basis. It should also be made a point that not only the employee signs this form but it should also be signed by the employer, which implies verbal and written protection against legal remedy to help protect the loss of time.
Hope the above will definitely help you inquire before you suggest anything on at-will employment.