CHICAGO (CBS) – A women’s group has filed a complaint against the Chicago Public Schools, claiming boys have more opportunities to play sports than girls.

CPS does field girls’ sports teams, but the National Women’s Law Center says it’s only a small percentage.

The Washington, D.C.-based advocacy group is suing 12 school districts across the country. The group says district data indicates there is a double-digit gap between the total number of female students in each school district and the number of female athletes, the Chicago Tribune reported.

The complaint by the group says the gap is 33 percentage points in CPS high schools, the highest among all schools they have cited, the Tribune reported.

The law center claims the disparity means CPS is in violation of Title IX, the 1972 federal law that forbids discrimination in education programs that take in federal funding, the Tribune reported.

CPS has yet to comment on the complaint, which is being reviewed by its attorneys.