Can a school hold your diploma over uniform?

The school is demanding that all of the graduated students to dry clean clothes or else does not receive their diploma. It was never any type of requirement they're just being petty. They clearly said in the beginning of the school year to return the uniform the same way you'd received it and I received mine dirty and wrinkled. I washed it and fold it but for some reason they're holding all diplomas until you do as they say...