The Chicago public school system plans this summer to at least double the number of schools where building services are privately managed, but isn't saying yet how many district workers will lose their jobs in the process or how much money it expects to save through the move.

The Chicago Sun-Times reports that the district sent a letter to building engineers saying it would fully move to private management by summer 2018. That means more than 500 engineers could lose their jobs, and if hired back, would move into a separate union for private-sector workers.

The school system already contracts with SodexoMagic and Aramark to oversee custodial services in schools, but principals and teachers have complained that their buildings are less clean since custodians were privatized.

Building engineers in Chicago are in charge of each school’s boiler, heat and other major infrastructure. Many of them are responsible for more than one building.