President Donald Trump has pledged to repeal a 50-year-old tax law that prohibits churches and other tax-exempt organizations from participating in political campaigns. If successful, the repeal could deal a major blow to the separation of church and state.

In an address to politicians and religious leaders gathered for the National Prayer Breakfast on Thursday, Trump declared: “I will get rid of and totally destroy the Johnson Amendment.”

The Johnson Amendment is a provision in the U.S. tax code named for Lyndon B. Johnson, who introduced it in Congress while he was still a senator. Congress /www.irs.gov/uac/charities-churches-and-politics"}}">passed the amendment in 1954, banning 501(c)(3) organizations ― which includes churches and charities ― from engaging in political campaign activity. Such activity includes publicly endorsing and opposing candidates, contributing to campaign funds and distributing materials in favor or opposition of any candidate.

The Internal Revenue Service upholds the prohibition accordingly, investigating churches and faith leaders who use their tax-exempt platforms to engage in political organizing of this nature.

The amendment aims to preserve an already precarious church-state divide by limiting religious organizations’ ability to sway elections. But for Trump, repealing the amendment appears to be an issue of religious freedom. At Thursday’s event, the president claimed the law undermines Americans’ “right to worship according to our own beliefs,” thus conflating political campaigning and religious worship.

Trump could propose changes to the current tax code, but only Congress has the power to officially repeal the amendment. But the president could effectively nullify the law by directing the IRS not to enforce it, tax law professor David Herzig told The Washington Post. The GOP currently holds a majority in Congress.

Progressive Christian author Jim Wallis tweeted about Trump’s comments on Thursday:

Trump wants to give the Religious Right what it has always wanted: the ability for congregations to be openly partisan in our elections. — Jim Wallis (@jimwallis) February 2, 2017

Many Republicans favor repealing the amendment. Ahead of last year’s Republican National Convention, the GOP’S official platform included a proposal to overturn the law.

Jerry Falwell Jr., the president of Christian-based Liberty University who was recently appointed to head Trump’s education task force, said at the time: “This is going to create a revolution among Christian leaders, nonprofit universities, and nonprofits in general.”

According to a 2014 Pew Research poll, nearly 60 percent of Republicans believe churches should express their political views, compared with 42 percent of Democrats. Just 38 percent of Republicans and 28 percent of Democrats, though, think churches should go as far as endorsing candidates.

Among the leaders and organizations, like Falwell, who favor repealing the amendment but maintaining religious organizations’ tax exemption, are conservative Christian nonprofit Alliance Defending Freedom, Catholic anti-abortion organization Priests for Life, and Branch Ministries Inc., whose permit the IRS revoked in the mid-1990s for campaigning against Bill Clinton.

Opponents of the Johnson Amendment argue that the law violates religious leaders’ First Amendment rights. Faith leaders, however, are allowed to endorse candidates and otherwise participate in political campaigns as private citizens, as long as they don’t claim to be speaking on behalf of their religious organization. Those in favor of upholding the law feel it maintains the integrity of the tax system under which churches and nonprofits do not pay taxes on their income and contributions made to them are tax-deductible by donors.

“Politicizing churches does them no favors. The promised repeal is an attack on the integrity of both our charitable organizations and campaign finance system," said Amanda Tyler, executive director of the Baptist Joint Committee, in a statement.

Religious leaders and organizations have long held tremendous sway in the U.S. political arena. The Christian right, also called the religious right, has proven to be a particularly powerful organizing force in recent decades, spearheading the movements against abortion and gay rights, as well as so-called “religious liberty” cases that allow businesses to discriminate against LGBT people. A leaked draft of an executive order on “religious freedom” suggests Trump may be mulling additional measures to fortify the Christian right.

Despite mounting support for repealing the Johnson Amendment, previous efforts to do so -- in 2013 and again in 2015 -- failed in Congress. As the Los Angeles Times wrote in a 2013 editorial: “Churches may have a 1st Amendment right to endorse candidates, but there is no constitutional right to a tax exemption.”