Obamacare was attacked by Republicans for spiking insurance premiums. But those costs could go up even more under the Republicans' own health care plans, and the middle class isn't immune.

Billions of dollars in federal subsidies that have reduce out-of-pocket expenses for over six million patients under Obamacare would be repealed by 2019 under the Senate health plan that was unveiled on Thursday.

That alone would send premiums shooting up by double digits for many, according to insurers' proposals submitted in expectation of the subsidies being eliminated.

Hardest hit will be millions of middle-income earners who make too much to qualify for premium assistance and will have to bear the full impact of any rate hikes. Those increases could be from 4.6 percent for small group plans in Oregon, to 22.9 percent in North Carolina. In Maryland, the state's largest insurers could increase premiums by 52 percent, the insurance group said.

Related: Senate Healthcare Bill Includes Deep Medicaid Cuts

"Subsidy changes would require some modest income individuals and families to pay much more for coverage, particularly those over age 50, and those living in high cost areas," said Karen Pollitz, a senior fellow with the independent, non-profit Kaiser Family Foundation. The repeal of cost-sharing subsidies would, she said, "ensure that deductibles and other cost sharing will increase for most non-group market participants."

Several medical groups were quick to denounce the newly unveiled Senate bill.

"Millions would lose insurance coverage altogether, women would be denied access to the provider of their choice, and many would face skyrocketing premium costs," said Dr. Haywood Brown, president of the American Congress of Obstetricians and Gynecologists, in a statement."Hardworking women and families would return to the days when having a child or facing a devastating diagnosis could mean bankruptcy."

However, the conservative Heritage Foundation said that shrinking Medicaid funding, getting rid of mandates and repealing Obamacare's taxes on the wealthy "will help reduce premiums and improve the environment that contributed to unaffordable (and now disappearing) health plans."

Related: Public Overwhelmingly Disapproves of New Healthcare Bill

What Can You Do?

Should the bill become law, patients not covered by an employer's insurance will need to figure out what's a better deal.

"Those who are in the marketplace now, or who expect to need to buy non-group coverage on their own in the near future, can look at the relative cost of coverage, the current law versus the Affordable Health Care Act," said Kaiser's Pollitz. "It will vary a lot based on a person’s age, income, and where they live."

The foundation plans to release an online calculator in the coming days to review the impact of the proposed bill.