The influential pro-Israel group AIPAC is asking supporters to back recently-drafted legislation that seeks to punish a peaceful movement in solidarity with Palestinians.

The organization, which is in Washington this week for an annual policy conference, is dispatching members to lobby lawmakers to pass the bill. One Washington-based group decrying Israel’s occupation of Palestine has said the proposal is unconstitutional.

“This dangerous bill seeks to impose fines on corporations that boycott business dealings with illegal Israeli settlements,” said Josh Ruebner, the policy director of the US Campaign for Palestinian Rights.

The organization also said Tuesday that the legislation would levy fines on companies that “divest assets from corporations profiting from settlements.” Text of the bill has not yet been posted on the Library of Congress website.

“It also seeks to deny Export-Import Bank loans to corporations that similarly boycott or divest from such business dealings,” Ruebner added. He said the bill violates Americans’ “First Amendment right to promote boycott, divestment and sanctions.”

The initiative, known as the BDS movement, was launched in 2005 by a wide swath of Palestinian civil society. It calls on people and institutions to boycott, divest from, and sanction Israel, until the occupation of Palestine ends.

That appeal includes calls for Israel to grant equal rights to its Arab and Palestinian citizens, and the right of return for Palestinian refugees.

AIPAC stands for the American Israel Public Affairs Committee. Its annual policy conference in Washington typically attracts many lawmakers, with the group claiming that “more than two-thirds of Congress” are present for the affair.

Since 2015, Congress has passed two trade bills that include anti-BDS language. One forces the US government to report on BDS activities, the other called on the US Trade Representative to advance anti-BDS initiatives in negotiations with European counterparts.

They received some opposition from the Obama Administration, due to their treatment of Israeli settlements. Language in both bills treated equally “Israeli-controlled territories” and Israel, in contradiction with longstanding US policy.

Original sponsors of one of those bills are backing the senate version of the legislation seeking to levy fines on BDS supporters.

Sens. Ben Cardin (D-Md.) and Rob Portman (R-Ohio) introduced their proposal last Thursday. It currently has five cosponsors, including three Democrats: Bob Menendez (D-N.J.), Richard Blumenthal (D-Conn.), and Bill Nelson (D-Fla.).

The House version of the legislation was also introduced last Thursday, by Reps. Peter Roskam (R-Ill.) and Juan Vargas (D-Calif.). It currently has 14 cosponsors, including eight Democrats.

Though US support for Israel, in recent years, has been strongly bipartisan, that has become drastically less true since 2014. After the Israeli military conducted a bombing campaign in Gaza that killed more than 1,500 Palestinian civilians, support for Israel fell dramatically among left-leaning Democrats.

Liberal and moderate Democrats combined are now roughly split in their sympathies for Israelis and Palestinians, according to a January poll. Sympathies for Israel had been ten points higher among all Democrats, just months before the survey.