(WASHINGTON) – Two major U.S. health insurance groups on Friday called on Senate Republican leader Mitch McConnell to drop from a healthcare bill a provision proposed by Senator Ted Cruz that allows insurers to offer stripped-down, low-cost healthcare plans.

“It is simply unworkable in any form and would undermine protections for those with pre-existing medical conditions, increase premiums and lead to widespread terminations of coverage for people currently enrolled in the individual market,” America’s Health Insurance Plans and the Blue Cross Blue Shield Association said in a letter to McConnell and Senate Democratic leader Chuck Schumer.

McConnell has planned for a vote next week on revised legislation, unveiled on Thursday, and he has his work cut out for him in the coming days to get the 50 “yes” votes needed for passage. Republicans control the Senate by a 52-48 margin and cannot afford to lose more than two from within their ranks because of united Democratic opposition, but two Republican senators already have declared opposition.