Almost every state in the U.S., including Wisconsin, is an at-will employment state. This means that absent any federal or state law violation, either the employer or the employee can terminate the employment relationship for any reason at any time. To add a bit more definition to employment relationships, many employers use employment contracts. However, contracts are only enforceable if their contents do not violate any laws.
Both companies and employees are bound by the contents of a signed job agreement. The elements of the contract can sometimes extend past a worker's last date of employment, if the parties agree to certain provisions in a severance package. An employment contract remains in effect until the provisions are satisfied.