Charter school parents are trying again to have a say in a lawsuit that they say could shut down some of their schools.

Parents Ken Ross, Jr. and LeDiva Pierce filed an appeal in federal court Tuesday to have a say in an ongoing desegregation lawsuit. St. Louis Public Schools is attempting to recover about $50 million that has gone to charter schools through the city’s desegregation tax, which the district argues was started to fund district school programs, not charter schools.

Charter school advocates have said the lawsuit, if successful, could force the closure of several charter schools who are unable to return the money in the course of one year.

The parents’ first attempt to join the legal battle was struck down in July by U.S. District Court Judge Henry Edward Autrey. Parents were denied a part in the legal battle because charter schools are not named as a party in the lawsuit, because they did not exist in St. Louis yet when the desegregation tax began.

Charter schools currently educate about one-third of public school students in the city.