A Georgia Supreme Court ruling that charter schools are exempt from contributing to Atlanta Public Schools’ pension costs is a “credit negative” for the school system, according to Moody’s credit rating service.

Moody’s said in its weekly credit outlook Monday that the ruling means less money is available for APS to pay its $550 million pension liability, and other school districts could also be affected because they can’t offload legacy costs onto charter schools.

Moody’s didn’t downgrade Atlanta Public School’s bond rating, but the assessment of the court ruling is one of many credit factors affecting the school system.