Republicans in the U.S. House of Representatives released their plan to repeal and replace the Affordable Care Act (ACA) on Monday, drawing criticism from Democratic lawmakers as well as some members of the Senate GOP.

AP Photo/Carolyn Kaster - apimages.com

The repeal would require 218 votes in the House and 51 votes in the Senate, and passage is no sure bet given complaints that have already surfaced from both wings of the Republican Party.

Here's what you need to know about the House GOP repeal and replacement plan.

• It would remove penalties for people who do not have health care insurance — effectively eliminating the ACA mandate.
• It would replace healthcare subsidies, and instead provide tax credits based on earnings, age, and family size.
• States that opted into Medicaid expansion under the ACA would be able to continue enrolling people until January 1, 2020. Then there will be a "freeze" on Medicaid expansion.
• Certain provisions of the ACA will be preserved. No insurer will be able to deny someone coverage due to a pre-existing condition and people will be able to stay on their parents' health care plan until they're 26.
• It would cut funding to Planned Parenthood, "rendering the women’s health organization ineligible for Medicaid reimbursements or federal family planning grants," The Washington Post reported.

Republicans whose constituents have benefited from Obamacare bristled at the Medicaid freeze.

Four GOP senators — Sens. Rob Portman (R-Ohio), Shelley Moore Capito (R-W.Va.), Cory Gardner (R-Colo.) and Lisa Murkowski (R-Alaska) — released a letter addressed to Senate Majority Leader Mitch McConnell Monday, expressing dissatisfaction with the plan's Medicaid policy.

"We believe Medicaid needs to be reformed, but reform should not come at the cost of disruption in access to health care for our country’s most vulnerable and sickest individuals," the senators wrote. "Any changes made to how Medicaid is financed through the state and federal governments should be coupled with significant new flexibility so they can efficiently and effectively manage their Medicaid programs to best meet their own needs."

As it is currently written, however, the senators said the plan "does not meet the test of stability for individuals currently enrolled in the program and we will not support" the replacement.

That's four GOP senators who have already come out against the plan, bringing the number of Republican lawmakers who could be trusted to vote in favor of the law down to 48.

J. Scott Applewhite/AP - apimages.com

More conservative members have already criticized the tax credits.

In addition to convincing at least two of those senators to support the replacement plan, Republican leadership would also have to assuage concerns voiced by three other conservative members of Congress: Sens. Mike Lee (R-Utah), Rand Paul (R-Ky.), and Ted Cruz (R-Texas), according to The New York Times.

"Still have not seen an official version of the House Obamacare replacement bill, but from media reports this sure looks like Obamacare Lite!" Paul wrote on Twitter Monday.