A federal judge in Washington is weighing whether to force a Chinese unit of a financial services powerhouse to appear in court in a potential billion-dollar securities fraud investigation.

The U.S. Securities and Exchange Commission said in September it wants the Shanghai unit of Deloitte Touche Tohmatsu Ltd., the audit, tax and financial services firm, to turn over documents regarding its work for a Cayman Islands-based company called Longtop Financial Technology Ltd.