Rep. Ted Lieu (D-Torrance) and 42 members of Congress are asking Atty. Gen. Loretta Lynch for a full Justice Department investigation into whether there is a pattern behind several Chinese American scientists being arrested in the U.S. on espionage charges.

Recently, National Weather Service employee Sherry Chen of Ohio and Temple University physics professor Xi Xiaoxing of Penn Valley, Pa., were arrested on suspicion of espionage. Charges in both instances were dropped with little explanation before going to court.

Lieu’s letter, which is scheduled to be sent Thursday, requests that Lynch open a full Department of Justice investigation into whether race, ethnicity or national origin played a part in recent cases in which Asian Americans have been arrested and indicted on espionage charges only to have those charges dropped.

Fears that the Chinese government is collecting U.S. trade and government secrets has led the Obama administration to aggressively investigate and prosecute suspected espionage, including urging federal employees to report suspicious behavior.

Lieu, who was born in Taiwan, said there is a threat of going too far and wrongly accusing Americans of betraying their country because of their skin color.

“The one thing that is the same fact among all of these is that they are all Asian American,” he said. “In my opinion there is now a pattern of practice. Maybe you have one case it’s a mistake, but when you have four or five cases now, to me that is a pattern. I want to know why that is.”

Lieu, the Democratic freshman class president, said he wants the investigation to look at whether there was enough evidence to arrest and indict the scientists in the first place, and what role bias and fears about Chinese espionage might have played.

Chen was accused of using a stolen password to access information about dams and passing the information to Chinese officials. Xi was accused of sharing with China schematics for a sensitive U.S.-made pocket heater used in superconductor research.

Eighteen members of California’s congressional delegation signed the letter. Signers include leaders of the Congressional Hispanic Caucus, the Congressional Black Caucus and the Democratic Caucus.

“Specifically, we request that you address why there appears to be an ongoing pattern and practice of people of color being singled out by federal law enforcement and prosecutors,” the letter states.

Lieu sent a similar letter in May after Chen’s arrest, to which the Justice Department responded by saying her ethnicity wasn’t a factor.

“We have received assurances from the [U.S. Attorney’s Office for the Southern District of Ohio] and the Federal Bureau of Investigation that Ms. Chen’s race played no role in the handling of her case,” it states.

On Wednesday, Lieu called the department’s response “rather perfunctory.”

"They came back with a rather short letter ... which basically says, 'Well, we asked the FBI and the prosecutors if they discriminated, and they said no,' " Lieu said. "We could have done that too. We want an independent investigation."