“Express advocacy” comes up in Akins v. Federal Election Commission:

Supreme Court precedent indicates that for a communication to constitute “express advocacy,” it must “in express terms advocate the election or defeat of a clearly identified candidate for federal office” by using words “such as ‘vote for,’ ‘elect,’ ‘support,’ ‘cast your ballot for,’ ‘Smith for Congress,’ ‘vote against,’ ‘defeat,’ ‘reject.'” Buckley, 424 U.S. at 44 & n.52. In Federal Election Commission v. Massachusetts Citizens for Life, the Court found that a publication that “urges voters to vote for ‘pro-life’ candidates” and “identifies and provides photographs of specific candidates fitting that description” constituted express advocacy, even though “this message is marginally less direct than ‘Vote for Smith. ‘” 479 U.S. 238, 249 (1986) (“MCFL“). In contrast, in Federal Election Commission v. Christian Coalition, the District Court found that a communication including both a scorecard with candidates’ voting records and a cover letter explaining that the scorecard ”’will give America’s Christian voters the facts they need to distinguish between GOOD and MISGUIDED Congressmen'” was not express advocacy. 52 F. Supp. 2d 45,64-65 (D.D.C. 1999) (quoting cover letter). The District Court in Christian Coalition also found that explicit directives such as “stand together,” “get organized,” and “start now,” all for the purpose of “making our voices heard in the elections” fell short of express advocacy. Id. at 64.

The court went on to discuss the communications at issue in the case (starting at p. 23 of the PDF).