Six centrist Republicans wrote President Obama Thursday, asking him to overturn regulations put in place during the Bush administration that limit funding for embryonic stem cell research.

Reps. Michael Castle (Del.), Charlie Dent (Pa.), Mark KirkMark Steven KirkThe Hill's Morning Report - Sponsored by Facebook - Senate makes SCOTUS nominee Barrett a proxy for divisive 2020 Senate Republicans scramble to put Trump at arm's length Liberal veterans group urges Biden to name Duckworth VP MORE (Ill.), Fred Upton (Mich.), Brian Bilbray (Calif.), and Judy Biggert (Ill.) asked Obama to act more quickly to reverse the Bush administration policy funding only a limited number of existing stem cell lines.

"We thank you for your support of the Stem Cell Research Enhancement Act, and your campaign commitment to stem cell research," the lawmakers wrote, "and hope you will now act to revoke President Bush's prohibition on federal funding for research involving embryonic stem cell lines derived after August 9, 2001 and to require that the National Institutes of Health issue appropriate guidelines."

The letter expresses somewhat of an open rift between the centrists and the conservative faction of the Republican Party.

In the 110th Congress's vote to overturn the Bush administration policy, only 11 of 193 voting Republicans expressed support for overturning the ban on additional funding.

"While we have been encouraged by recent news reports that you plan to issue an Executive Order soon, we cannot stress enough the importance of swift action," the letter read. "After the current restrictions are lifted, we stand ready to work with you and our colleagues in Congress on adopting complimentary legislation."