Hoffman (defendant) hired Castro to operate machinery in its plant. Castro provided documents verifying his authorization to work in the United Sates before starting work. A year later, Hoffman laid off Castro and three other employees who were known union supporters. The National Labor Relations Board (NLRB) found that Hoffman had laid off the employees in violation of the National Labor Relations Act (NLRA) and ordered that Hoffman offer reinstatement and back pay. At a hearing before an administrative law judge to determine the amount of back pay, Castro admitted that he fraudulently obtained a driver’s license and Social Security card and was not authorized to work in the United States. The judge found that back pay could not be awarded to Castro because of the Immigration Reform and Control Act (IRCA), which makes it unlawful for employees to use fraudulent documents to show work authorization. Four years later, the NLRB determined that back pay should be ordered from the date of termination to the date Hoffman first learned that Castro was not authorized. Hoffman filed a petition to review with the Court of Appeals, which denied the petition twice. The Supreme Court granted certiorari on Hoffman’s appeal.