South Carolina has become the first state to enact legislation aimed at thwarting an international pro-Palestinian economic and disinvestment campaign intended to penalize Israel. Illinois will soon become the second, and advocates say plans are underway for similar laws in 18 more states.

In Washington, Congress could vote this month on trade legislation with language that would encourage the blacklisting of foreign companies that support the pro-Palestinian campaign, known as Boycott, Divest and Sanction, or B.D.S. The trade legislation is notable in part because the scope of its blacklisting could include companies that refuse to do business with Israeli settlements in the occupied territories, even though they are widely considered illegal.

And in Las Vegas this weekend, Sheldon Adelson, the multibillionaire casino owner who is one of the Israeli government’s most important American supporters, is convening a private meeting of pro-Israel donors to devise new strategies for countering B.D.S., particularly on American college campuses, where it has gained some support since the Gaza war last summer.

Alarmed over what they see as the growing influence of B.D.S., Israel’s advocates in the United States, mirroring the reaction among many in Israel, are scrambling to respond. Some have embraced a call by the new Israeli justice minister, Ayelet Shaked, to “boycott the boycotters.”