New Yorkers seeking reimbursement from insurance carriers may face greater challenges if Governor Spitzer’s tax proposal for private health maintenance organizations is enacted.

In the budget he presented to lawmakers yesterday, Mr. Spitzer proposed taxing for-profit HMOs at the same rate as other health insurers. If enacted, the HMOs would be subjected to a 1.75% premium tax, instead of a 7.5% income tax, a cost that consumer advocates warned could be passed on to policyholders.

“Eventually, it would funnel down,” a spokeswoman for the insurance carrier Aetna, Susan Millerick, said. “The people with the highest burden would be people buying individual plans and small group plans.”

With the state facing a projected $4.4 billion budget gap, changing the tax status of HMOs could generate $247 million in revenue. In a separate measure, Mr. Spitzer also proposed increasing the “covered lives assessment” on health insurance carriers by $140 million to $990 million.

As a candidate and as governor, Mr. Spitzer has said he would not raise taxes, and yesterday he stressed that his budget proposal would close existing tax loopholes.

In the case of HMOs, Mr. Spitzer said the proposal is to make companies “pay their fair share.”

“It’s a matter of pure horizontal equity,” he said.

Historically, HMOs were exempt from the taxes imposed on traditional health insurance carriers because many of the companies started off as nonprofit entities. Today, many are for-profit corporations that generate significant revenues. Oxford Health Plans generates $5 billion in annual premiums, according to the New York State Insurance Department.

“It’s an anomaly that the HMOs are taxed on the basis of their income, where insurance companies that sell essentially identical products are taxed the same way that all insurance companies in the state other than HMOs are taxed, which is on the basis of their premiums,” director of the budget and a senior advisor to Mr. Spitzer, Paul Francis, said.

The health insurance industry and some elected officials offered a different perspective.

“They’re going to pass through these costs,” the majority leader of the state Senate, Joseph Bruno, said at a news conference. “It’s going to be a pass-through to people who are already having trouble paying for health insurance.”

“It is what we would consider a tax on health care,” the Business Council of New York State’s director of corporate affairs, Mark Amodeo, said. “It’s a tax that will be reflected in higher health insurance premiums. It will add to the cost of coverage and ultimately to the cost of doing business in New York.”

The health insurance industry also warned that costs would be passed to consumers.

“The Governor says he is asking the health insurance industry to ‘pay their fair share,'” the president and CEO of the New York Health Plan Association, Paul Macielak, said in a statement. “We think he’s asking insurers to pay more than their fair share.”

In his budget proposal, Mr. Spitzer also called for $980 million in Medicaid and other health care cuts.