The conservative House Freedom Caucus on Wednesday endorsed a revised version of a bill backed by GOP congressional leaders and the White House that would allow states to opt out of a core ObamaCare protection that prevents insurers from denying coverage to people with pre-existing conditions.

Conservatives have complained the provision drives up premiums.

The agreement with the most conservative Republicans puts moderates in a pickle. They have demanded that the popular protection remain in any legislation to replace the Affordable Care Act but now may in the uncomfortable position of being the only obstacle to passing and enacting Obamacare replacement legislation.

The change to the GOP plan was negotiated by centrist Rep. Tom MacArthur, R-N.J., and Freedom Caucus Chairman Rep. Mark Meadows, R-N.C.

"The MacArthur amendment will grant states the ability to repeal cost driving aspects of Obamacare left in place under the original AHCA. While the revised version still does not fully repeal Obamacare, we are prepared to support it to keep our promise to the American people to lower healthcare costs," The Freedom Caucus said in a statement. 

The group of hard line conservatives voted against a previous repeal and replace bill last month. 

Insurers and hospital stocks were moving slightly. Humana (HUM - Get Report) was up about 1.5% to $219.50 per share, . Cigna (CI - Get Report) and Aetna (AET) were both up less than a percent.

Hospital stocks were mixed with Community Health (CYH - Get Report) down about 1.25% to $8.49, HCA (HCA - Get Report) was down about 1.1% and LiePoint LPNT down about 20 cents to $61.30 per share. Tenet (THC - Get Report) was up about 4 cents, or .2%, to $15.63 per share. 

Editor's note: This story was originally published at 1:35 p.m. ET on April 25 and has been updated to include market movers.