The U.S. Treasury Department has rebuffed a request by House Ways and Means Chairman Rep. Paul Ryan, R- Wis., to explain $3 billion in payments that were made to health insurers even though Congress never authorized the spending through annual appropriations.

At issue are payments to insurers known as cost-sharing subsidies. These payments come about because President Obama’s healthcare law forces insurers to limit out-of-pocket costs for certain low income individuals by capping consumer expenses, such as deductibles and co-payments, in insurance policies. In exchange for capping these charges, insurers are supposed to receive compensation.