Pulpit Freedom Sunday is an initiative started in 2008 by the Alliance Defending Freedom, a conservative Arizona-based non-profit focused on defending religious liberty.
"The ultimate goal of Pulpit Freedom Sunday is to restore a pastor's right to speak freely from the pulpit without fearing government censorship or punishment," said Erik Stanley, senior counsel at Alliance Defending Freedom. "The IRS currently holds the power to impose legal sanctions on a church for something its pastor preaches from the pulpit."
As a senator, Lyndon B. Johnson backed a change in the US tax code that blocked some tax-exempt organizations, including churches, from supporting or opposing political candidates.
"Until 1954, America's pastors had the right to speak freely they exercised that right responsibly," Stanley said. "Churches were not turned into political action committees and party bosses did not set up shop in the basement of churches. Instead, pastors spoke out as they believed their faith intersected with something that was happening in an election. Pastors should have the right to decide that issue for themselves."
Republican presidential nominee Donald Trump has pledged to repeal the "Johnson Amendment" should he win.
"The Johnson Amendment has blocked our pastors and ministers and others from speaking their minds from their own pulpits," he said at the Values Voter Summit last month.
"If they want to talk about Christianity, if they want to preach, if they want to talk about politics, they're unable to do so. If they want to do it, they take a tremendous risk that they lose their tax-exempt status," he said. "All religious leaders should be able to freely express their thoughts and feelings on religious matters. And I will repeal the Johnson Amendment if I am elected your president, I promise. So important."
Hillary Clinton campaign did not respond to CNN's request for comment on the Johnson Amendment.
The IRS told CNN that federal privacy laws prohibit the agency from commenting on any individual taxpayer or case.
But Jim Garlow, lead pastor of Skyline Church in San Diego, has tried to get the IRS to comment on this issue for years.
"We record our sermons, as have many several thousands of pastors, and then send their sermons to the IRS in the hopes of provoking a lawsuit. But we have not been successful," he said.
Although ADF advocates for more traditional social issues like marriage and abortion, the group is not endorsing a candidate or encouraging pastors to address certain issues.
"ADF remains firmly committed to the goal that Pulpit Freedom Sunday is not about any particular issue or candidate or election, but is about restoring the right of pastors to speak freely from their pulpits and removing the censorship and punishment power from the IRS," Stanley said.
Trump supporter Tony Perkins, president of the socially conservative Family Research Council, said that although pastors don't need to choose a candidate, they do need the freedom to do so if they want.
"As a pastor, you have a biblical responsibility to speak to your congregation and help them understand the issues and how they line up with Scripture," he said. "We're simply going down the list of biblical issues like life and human sexuality and marriage and speaking to what Scripture has to say and juxtaposing that with the positions of the candidates."
But not all clergy are in favor of religious leaders using the pulpit to make political endorsements.
Broderick Greer, curate at Grace-St. Luke's Episcopal Church in Memphis, Tennessee, believes support for Pulpit Freedom Sunday is due to more conservative leaders losing influence in an increasingly diverse climate.
"I don't see our relationship with the people we're serving as one of paternalism," he said. "I would never want to tell people who they should vote for."
"If you want to lose your tax-exempt status, then feel free to make an endorsement from your pulpit. If you don't then, you don't," he added. "I think the broader question is should religious organizations have tax-exempt status at all."