WASHINGTON (AP) — The Education Department withdrew recognition of the nation’s largest accreditor of for-profit colleges on Thursday, a decision that could force schools to close and threaten financial aid to hundreds of thousands of students.

The Accrediting Council for Independent Colleges and Schools said it would appeal the decision to Education Secretary John B. King Jr. Interim President Roger Williams said the council planned “to continue diligent efforts to renew and strengthen its policies and practices” to meet the department’s criteria for accreditors.

The accrediting agency has been accused of lax oversight of its schools, which included those once owned by the now-defunct Corinthian Colleges Inc. and the recently shuttered ITT Technical Institute.

In a letter to the agency, Emma Vadehra, King’s chief of staff, said “ACICS’ track record does not inspire confidence that it can address all of the problems effectively.”

Vadehra said the department found fundamental problems with the council’s functions as an accreditor. Her decision followed staff and advisory panel recommendations to sever ties with the council.

If ACICS loses its appeal, hundreds of schools would be forced to find a new accreditor within 18 months or lose their ability to participate in federal financial aid programs, such as student loans and Pell Grants. About 600,000 students currently attend ACICS-accredited institutions, Williams said.