If an individual without good cause fails to apply for and undergo vocational rehabilitation when so directed under section 8104 of this title, the Secretary, on review under section 8128 of this title and after finding that in the absence of the failure the wage-earning capacity of the individual would probably have substantially increased, may reduce prospectively the monetary compensation of the individual in accordance with what would probably have been his wage-earning capacity in the absence of the failure, until the individual in good faith complies with the direction of the Secretary.