Under the Federal Railroad Safety Act, the employer violates the Act’s anti-retaliation provision if a discharge of an employee due even “in part” to the employee’s refusal to violate or assist in violating a railroad safety law, rule, or regulation. Hence, the employer is not entitled to summary judgment on such a claim simply by proving it had good cause (apart from retaliation) for the discharge. That merely shows the employer “could” have properly discharged the employee for non-retaliatory reasons. Instead, the employer must show by clear and convincing evidence that it would have fired the employee even if he had not engaged in the protected activity.