Even if you are an at-will employee, there are laws enacted that prevent employers from firing you in certain situations such as:
Employees who are in a protected class:
Under the law, employers are prohibited from firing employees simply because of their race, age, gender, marital status, religion, disability, national origin, or pregnancy.
Employees who request leave under the FMLA:
Employers are also banned from firing employees who lawfully request or take leave under the Family and Medical Leave Act.
Employees who refuse to endure hostile work environments:
An employee also cannot be terminated simply because he or she fails to adhere to quid pro quo sexual harassment advances or work in a hostile environment.
Employees who refuse to work amidst illegal, unsafe conditions:
There are certain laws (such as the Occupational Safety and Health Act) that also protect employees from working in unsafe conditions that jeopardize their health. An employer cannot fire an employee for refusing to work in such conditions.
Employees who report violations of employment laws:
Often referred to as whistle-blowing, employees who report illegal wage and hour or other criminal practices by their employers cannot be terminated for doing so.