Two of the nation’s largest health care insurance companies called on the Senate to strike an amendment by Sen. Ted Cruz to their health care bill, saying it would “undermine protections for those with pre-existing medical conditions.”

Cruz’s amendment to the Better Care Reconciliation Act would allow insurers to sell low-cost policies that don’t meet existing federal regulations so long as they also offer one plan that does include services required under the Affordable Care Act, such as prescription drug
coverage.

America’s Health Insurance Plans and the Blue Cross Blue Shield Association said the proposal was “unworkable in any form.” The health insurance companies sent a joint letter to Senate Majority Leader Mitch McConnell Friday afternoon expressing their concerns that people on the individual market would lose coverage and premiums would rise.

Prior to this letter, the two insurance groups expressed problems with the amendment in separate statements.

The condemnation comes as McConnell works to persuade both conservative and moderate Republicans to back his plan to repeal and replace President Obama’s 2010 signature healthcare law.

McConnell delayed a vote on the revised health care bill after Sen. John McCain, R-Ariz., announced Friday he had undergone surgery for a blood clot behind his eye.

The Cruz amendment was included in the latest version of the Republican replacement bill as a way to push conservative holdouts toward supporting the plan.

“I am encouraged that the revised bill ensures consumers have the freedom to choose among more affordable plans that are tailored to their individual healthcare needs,” Cruz said in a statement.

The senator from Texas said his proposal would still require plans to meet state protection requirements, even if they don’t comply with regulations under Obama’s health care law. Tax-credits would continue to be provided for people using Obamacare-compliant plans.

The letter from the health insurance companies said this consumer freedom provision would drive up premiums as healthier people move to less-regulated plans, while those with pre-existing conditions would continue needing the comprehensive plans. The two groups said middle-income families would be especially impacted because they don’t qualify for the tax-credits.

The amendment could raise premiums for 1.5 million people with pre-existing conditions, according to a report released last week by the nonpartisan Kaiser Family Foundation.

The nonpartisan Congressional Budget Office was expected to publish an analysis of the updated bill early this week but said the release was postponed on Sunday. No further update has been provided.