From AID v. Open Society Int’l:

A comparison of two cases helps illustrate the distinction: In Regan v. Taxation With Representation of Washington, the Court upheld a requirement that nonprofit organizations seeking tax-exempt status under 26 U. S. C. §501(c)(3) not engage in substantial efforts to influence legislation. The tax-exempt status, we explained, “ha[d] much the same effect as a cash grant to the organization.”461 U. S., at 544. And by limiting §501(c)(3) status to organizations that did not attempt to influence legislation,Congress had merely “chose[n] not to subsidize lobbying.” Ibid. In rejecting the nonprofit’s First Amendment claim,the Court highlighted—in the text of its opinion, but see post, at 5—the fact that the condition did not prohibit that organization from lobbying Congress altogether. By returning to a “dual structure” it had used in the past—separately incorporating as a §501(c)(3) organization and §501(c)(4) organization—the nonprofit could continue to claim §501(c)(3) status for its nonlobbying activities, while attempting to influence legislation in its §501(c)(4) capacity with separate funds. Ibid. Maintaining such a structure, the Court noted, was not “unduly burdensome.” Id., at 545, n. 6. The condition thus did not deny the organization a government benefit “on account of its intention to lobby.” Id., at 545.

In FCC v. League of Women Voters of California, by contrast, the Court struck down a condition on federal financial assistance to noncommercial broadcast television and radio stations that prohibited all editorializing, including with private funds. 468 U. S. 364, 399–401 (1984).Even a station receiving only one percent of its overall budget from the Federal Government, the Court explained, was “barred absolutely from all editorializing.” Id., at 400. Unlike the situation in Regan, the law provided no way for a station to limit its use of federal funds to noneditorializing activities, while using private funds “to make known its views on matters of public importance.” 468 U. S., at 400. The prohibition thus went beyond ensuring that federal funds not be used to subsidize “public broadcasting” and instead leveraged the federal funding to regulate the stations’ speech outside the scope of the program. Id., at 399 (internal quotation marks omitted).