President Donald Trump, who is strongly backed by evangelical Christian voters, has promised to "totally destroy" a 1954 US law barring churches and other religious institutions from political activity if they want to keep tax-exempt status.
Trump made his comments about a measure called the Johnson Amendment during remarks at the annual National Prayer Breakfast on Thursday.
"I will get rid of and totally destroy the Johnson Amendment and allow our representatives of faith to speak freely and without fear of retribution. I will do that, remember," Trump told an audience including politicians, religious leaders and guests such as Jordan's King Abdullah.
The Johnson Amendment prohibits tax-exempt organisations such as churches, charities and educational institutions from directly or indirectly participating in any political campaign in favour or against a political candidate.
It is named after Democratic former President Lyndon Johnson and is an important statutory barrier between politics and religion.
A change in the law would require action in the Republican-led US Congress.
