"We write to urge you to examine whether, in the government's efforts to stop espionage, it may be rushing to judgment in investigations involving Asian Americans, primarily of Chinese descent," the Nov 18 letter said. "The Department of Justice's response has been to dismiss these concerns without addressing the underlying policies and practices that led to mistakes which precipitated these wrongful prosecutions of American citizens."

Forty-two members of Congress sent a letter to Lynch on Nov 5 about the cases. Congresswoman Judy Chu of California organized the Nov 17 press conference and was joined by three others US representatives at the Capitol Building.

"Similar to the recent request of 42 members of Congress calling for an investigation, we urge you to investigate whether federal investigators and prosecutors improperly overrelied on race in recent prosecutions, and to increase training and oversight over ongoing and future investigations and prosecutions against Chinese Americans for spying and espionage," the Nov 18 letter said.

"As the Department of Justice states in its 2014 guidance on the use of race, biased law enforcement practices 'have a terrible cost, not only for individuals but also for the nation as a whole'."

Both letters requested an independent investigation into whether race, ethnicity or national origin played a part in the recent cases.

The commission also cited the case of Wen Ho Lee, a nuclear engineer who was indicted in December 1999 on espionage charges. Lee had worked on the W-88 nuclear warhead at the Los Alamos National Laboratory in New Mexico. The indictment charged him with mishandling national security information after a document had surfaced in China in 1995 connected to the W-88. Lee was a suspect because he had visited Beijing and Hong Kong.

Investigators could not prove the initial charges, and a separate investigation resulted only in Lee being charged with improper handling of restricted data, one of the original 59 indictment counts, to which he pleaded guilty as part of a plea settlement.

In 2006, Lee received $1.6 million from the government and five media companies to settle a civil suit for the leaking of his name before charges had been filed. Federal Judge James A. Parker apologized to Lee in September 2000 for denying him bail and putting him in solitary confinement, and criticized the government's handling of the case.

Pan Jialiang in Washington contributed to this story.