The Johnson Amendment, which became law in the U.S. in 1954 and was named for Lyndon Johnson, then a U.S. Senator, “is a provision in the tax code that prohibits tax-exempt organizations from openly supporting political candidates. In the words of the tax code, ‘all section 501(c)(3) organizations are absolutely prohibited from directly or indirectly participating in, or intervening in, any political campaign on behalf of (or in opposition to) any candidate for elective public office.” I submit that it is in a cleric’s interest to expand this prohibition to include advocating for (or opposing) particular public policies. This general principle would of course be subject to exceptions in which a proposed or enacted policy is strongly anathema to the religious principles of the given religious organization or religion.
The full essay is at "Being Partisan in the Pulpit."
 Randall Balmer, “The Peril of Being Partisan at the Pulpit,” Stars and Stripes, February 7, 2017.