PROVIDENCE, R.I. - A Rhode Island teachers union has sued a troubled school district that fired all its high school teachers and staff. The union is challenging a requirement that all fired teachers reapply for their jobs.

No more than half can be rehired under a federal turnaround model selected for the school district. The union says it thought Superintendent Frances Gallo was committed to working with them on an alternative to the firings, which take effect at the end of the school year.

Instead, Gallo alerted teachers in letters last week they would need to reapply and present a five-minute lesson to get their jobs back. Central Falls High School has been identified as among the worst in the state. Gallo said she resorted to firings when talks with the union broke down.