A new lawsuit challenges the U.S. Department of Education’s “unlawful pause” on federal student loan payments that have cost taxpayers $150 billion from lost interest.

The lawsuit, filed in the U.S. District Court for the Eastern District of Michigan by the New Civil Liberties Alliance and the Mackinac Center for Public Policy, says Congress lawfully suspended monthly payments and interest accrual on federally held student loans for six months.

However, the lawsuit challenges the legality of the department unilaterally extending the deferment period 30 months past the statutory expiration date of September 2020 without Congressional approval.