https://mtsu.edu/first-amendment/article/1744/johnson-amendment
The Johnson Amendment is an addition, adopted in 1954, to the Internal Revenue Code, 501(c)(3). As a condition for maintaining exception from income taxes and other taxes, charitable organizations including churches and affiliated groups, were forbidden from participating or intervening in “any political campaign on behalf of (or in opposition to) any candidate for public office” (Davidson 1998, 17).
The amendment is named after then Senator (later President) Lyndon B. Johnson, who introduced the amendment out of concern about the Facts Forum and the Committee for Constitutional Government. Both were tax-exempt organizations that had imitated the tactics of Senator Joseph R. McCarthy (R., WI) in campaigning against politicians like Johnson who were more liberal in their political orientations.