The Census Bureau plans to ask people if they are U.S. citizens in the 2020 count of the nation’s population, igniting fears that the information could be used to target those in the country illegally.

Census officials said the question is being reinstated for the first time since 1950 to help enforce the Voting Rights Act and that there are safeguards in place to prevent any abuse of the information. It is illegal to release information that would identify individuals or families.

But that does not mean that census data has not been used to target specific populations in the past.

In fact, information from the 1940 Census was secretly used in one of the worst violations of constitutional rights in U.S. history: the internment of Japanese-Americans during World War II.

In papers presented in 2000 and 2007, historian Margo Anderson of the University of Wisconsin-Milwaukee and statistician William Seltzer of Fordham University found evidence that census officials cooperated with the government, providing data to target Japanese-Americans.

The Japanese-American community had long suspected the Census Bureau of playing a role in the push to banish 120,000 Japanese-Americans, mostly living on the West Coast, into nearly a dozen internment camps ­following the bombing of Pearl Harbor on Dec. 7, 1941, according to former Transportation and Commerce Secretary ­Norman Mineta.

Mineta, who lived in San Jose, was just 11 when he and his family were sent to live in an internment camp in Heart Mountain, Wyo. For decades, though, census officials denied that they had played any role in providing information.

According to Anderson and Seltzer, the Federal Bureau of Investigation and military intelligence agencies began pushing in late 1939 to relax census confidentiality rules in the hopes of accessing data on individuals. But the effort was opposed by Census Bureau Director William Lane Austin.

After the 1940 presidential election, however, Austin was forced to retire. He was replaced by J.C. Capt, who backed efforts to remove confidentiality provisions. Capt’s efforts helped clear the way for other agencies to access the information on Japanese-Americans.

In 2000, Anderson and Seltzer found documents that showed officials with the Census Bureau had provided block-level information of where those of Japanese ancestry were living in California, Arizona, Wyoming, Colorado, Utah, Idaho and Arkansas.

The revelations prompted Kenneth Prewitt, then Census Bureau director, to issue a public apology. He wrote: “The historical record is clear that senior Census Bureau staff proactively cooperated with the internment, and that census tabulations were directly implicated in the denial of civil rights to citizens of the United States who happened also to be of Japanese ancestry.”

Anderson and Seltzer, however, weren’t finished. They suspected that despite the bureau’s denials, it had also released “microdata” — information about individuals, including names and addresses.

In 2007, they found proof, uncovering documents that showed census officials provided names and addresses of individuals of Japanese ancestry in Washington D.C.

While the Census Bureau had no such record, the pair found the information in records kept by the Commerce Department’s chief clerk. Under the Second War Powers Act, which suspended the confidentiality protections for census data, the chief clerk had the authority to release census data to other agencies. That meant while the information released was not illegal, it was ethically questionable, the researchers said.

The Aug. 4, 1943, request was made by Treasury Secretary Henry Morgenthau. He had asked for the names and addresses of all individuals of Japanese ancestry living in Washington. Morgenthau had requested the information to aid in a Secret Service investigation of threats made against President Franklin D. Roosevelt.

In all, information about 79 people in Washington was released, the researchers found. The records did not indicate that personal information was released on Japanese-Americans living in other parts of the United States.

The mass-incarceration of Japanese-Americans, the majority of whom were American citizens, is now considered a stain on American history.

“The Census Bureau doesn’t like to talk about it,” said Prewitt, who served as director from 1998 to 2000. He recalled that when he spoke to a colleague about the issue, he received a terse “Well, it was legal” as a response.

“It was not illegal,” Prewitt added. “But it was certainly inappropriate. It was obvious that the Census Bureau facilitated the roundup of Japanese Americans.”