Charter schools are often promoted as a tool to address educational inequities, but a potential precedent-setting legal case launched this week says the opposite. In filings with the U.S. Department of Education, two Delaware nonprofit groups allege that some of the state's publicly funded, privately managed schools are actively resegregating the education system -- and in a way that violates federal civil rights law.

The complaint, by the Delaware branch of the American Civil Liberties Union and the Community Legal Aid Society, cites data showing that more than three-quarters of Delaware's charter schools are "racially identifiable" -- a term that describes schools whose demographics are substantially different from the surrounding community. According to the complaint, "High-performing charter schools are almost entirely racially identifiable as white" while "low-income students and students with disabilities are disproportionately relegated to failing charter schools and charter schools that are racially identifiable as African-American or Hispanic."

Elizabeth Lockman, an ACLU board member, told Delaware public radio that when her daughter enrolled in Wilmington public schools, she noticed a troubling change in the years since the civil rights movement first began its push for integration.

“I made the choice to put her in a neighborhood school in Wilmington, but I was just continually astounded by the amount of resegregation that had happened in the short period of time since I had been a high school student,” she told radio station WDDE.

Among the steps the groups are asking the Obama administration to take are prohibiting subjective admissions policies for charter schools and barring extra fees for attending charter schools -- factors they say effectively discriminate against low-income, disabled or minority students. Because the case is being filed with the Department of Education, such actions in Delaware could have implications for federal oversight of school districts across the country.

A spokesperson for one of the Delaware school districts targeted by the complaint told the News Journal that the district "is now and always has been committed to the principles of diversity and inclusion in our schools, and we will continue to be guided by those principles in providing a high-quality education to all our students."

The complaint lands amid mounting data tying charter schools to segregation.

In 2010, for example, a University of Colorado report analyzing charter schools from across the country found that "as compared with the public school district in which the charter school resided, the charter schools were substantially more segregated by race, wealth, disabling condition and language." Similarly, in reviewing a decade worth of research about charter schools, George Washington University education researcher Iris Rotberg earlier this year concluded that "charter schools often lead to increased school segregation ... and lead to the stratification of students who were previously in integrated environments."

Meanwhile, a General Accountability Office study in 2012 showed that "charter schools enrolled a lower percentage of students with disabilities than traditional public schools."

The potential causes of segregation aren't entirely clear. In the Delaware case, the groups blame charter schools' admissions requirements for effectively promoting discrimination.

"These requirements include high examination scores, essays written by parents to explain why a school is a good choice for their child, access to gifted and talented elementary and middle school programs that help increase academic performance, annual activities fees, mandatory parent involvement and mandatory high-cost uniform purchases," the ACLU said in a statement announcing the complaint. "Such barriers prevent students from low-income African-American and Hispanic families from having the same access to high-quality charter schools that middle- and upper-class families have."

In May, the Department of Education warned charter school administrators that not only must their admissions policies "be nondiscriminatory on their face," those policies "may not use admissions criteria that have the effect of excluding students on the basis of race, color or national origin."

Charter schools' defenders say some of the segregation trends may merely reflect geography.

"A naive examination ... appears to show that the critics are right: More choice is associated with minority students attending less diverse schools," wrote the Brookings Institution's Matthew M. Chingos in his 2013 study of education data. "Of course, this relationship ignores the fact that charters tend to locate in areas that serve large shares of disadvantaged students and members of minority groups. As a result, this simple correlation tells us nothing about whether charters increase segregation or just tend to locate in areas where the schools are already segregated."