Oregon regulators shut down the state's Obamacare consumer-oriented and operated plan, leaving only eight co-ops remaining nationwide.

Oregon's insurance regulator closed the co-op late Friday due to poor finances, meaning that 15 of the original 23 co-ops have collapsed. The closures have cost taxpayers more than $1.5 billion in startup and solvency loans.

Oregon's Health CO-OP was put in receivership on Friday and regulators gave its 20,600 policyholders until the end of the month to find a new plan.

"We understand changing plans in the middle of the year will be difficult for Oregonians, but this action was necessary given the sudden deterioration of the company's financial position," the regulator said Friday.

The co-op lost $18.4 million last year, mostly because of high claims from policyholders.

What also didn't help was Obamacare's risk-adjustment program, which transfers funds from insurers with healthy enrollees to insurers with the sickest claims.

The program required the Oregon co-op to pay out $900,000, while it was expected to receive about $5 million.

When the risk-adjustment payments were released on June 30, the 10 remaining co-ops at the time owed $150 million in risk-adjustment payments.

Since then, Connecticut's insurance regulator shut down the state's co-op, HealthyCT, which owed $13.4 million in risk-adjustment payments.

Republicans have lashed out at the administration over the co-op closures, saying that they are proof the healthcare law is unsustainable.

House lawmakers questioned how the administration plans to get back the $1.5 billion it has loaned out to the co-ops that have collapsed.

"The co-ops are going down faster than the Titanic, yet there is not enough urgency coming out of the Obama administration to protect taxpayer dollars," said Rep. Fred Upton, R-Mich., chairman of the House Energy and Commerce Committee. "With eight barely hanging on, what can the administration do to prevent further losses?"

The Centers for Medicare and Medicaid Services, which oversees the co-ops, said that it and state insurance regulators are working aggressively to ensure the co-ops are "well-run and financially sound."