Under the Federal Railroad Safety Act as amended by the Aviation Investment and Reform Act for the 21st Century, 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. The employee’s initial burden on a retaliation claim is slight and satisfied by proof that the protected activity played even a small part in the employer’s adverse employment action. However, here the trial court found, applying the correct clear and convincing evidence standard, that the employer had proven it would have taken the same adverse employment action even in the absence of the protected activity. Hence, judgment for the employer is affirmed.