A congressional oversight committee on Thursday accused New York of overbilling Medicaid by billions of dollars by inflating reimbursement payments to its state-run institutions for the mentally disabled.

In a scathing report, the Republican-led House Oversight and Government Reform Committee said New York overcharged taxpayers by $15 billion since 1990.

In 2011, New York charged a per-diem rate of $5,118 for residents of the institutions, a network of 11 centers that now house about 1,300 people with severe developmental disabilities. Over the course of a year, Medicaid spends $1.9 million for every resident, or $2.5 billion in total—with half coming from the federal government. But the cost of running the institutions is only a quarter of that amount.

The report said New York took advantage of a complex formula and kept federal officials in the dark for years. It also faulted the federal agency that oversees Medicaid for waiting years before investigating after becoming aware of the high payments.

"This is intentional fraud," said Arizona Rep. Paul Gosar, a Republican committee member.