The Justice Department has opened an investigation into the use of race in Harvard University’s admissions practices and has accused the university of failing to cooperate with the probe, according to documents reviewed by The Wall Street Journal.

The Justice Department is investigating complaints that formed the basis of a federal civil lawsuit filed in 2014 in Boston, according to the documents. That suit alleges Harvard intentionally discriminates against Asian-Americans by limiting the number of Asian students who are admitted.

The lawsuit, brought by a nonprofit called Students for Fair Admissions, said the practices violate federal civil-rights law and asks a federal judge to prohibit Harvard from using race as a factor in future undergraduate admissions decisions. The suit is pending.

The Justice Department, whose Civil Rights Division is conducting the investigation into similar allegations, said in a letter to Harvard’s lawyers, dated Nov. 17 and reviewed by the Journal, that the school was being investigated under Title VI of the Civil Rights Act of 1964, which bars discrimination on the basis of race, color and national origin for organizations that receive federal funding. The letter also said the school had failed to comply with a Nov. 2 deadline to provide documents related to the university’s admissions policies and practices.

The department told Harvard it “may file a lawsuit” to enforce compliance if Harvard doesn’t hand over the documents by Dec. 1, according to a separate letter dated Nov. 17 from John M. Gore, the acting assistant attorney general for the Civil Rights Division. The department wrote that the materials requested by the Justice Department have already been provided by Harvard to the plaintiffs in the lawsuit.