When an employee is terminated or laid-off, there are no regulations requiring employers to give advance notice to the employee unless the employee is covered by an individual contract with their employer or employees covered by a union/collective bargaining agreement.
In addition, the WARN Act provides for notice to workers prior to lay-off. The WARN Act required employers with more than 100 employees to provide notice 60 days in advance of covered plant closings and covered mass layoffs.
Also, some states may have requirements for employee notification prior to termination or lay-off. Check with your state department of labor for regulations in your state.