A bill that would criminalise boycotts against Israel has been signed by 45 US senators and 237 congressman.

The so-called “Israel Anti-Boycott Act” would impose fines of up to $250,000 (£192,000) on any US citizen “engaged in interstate or foreign commerce” who supports a boycott of Israeli goods and services.

The US has long defended Israel in territorial disputes in the Middle East, even as the Israeli military has expanded into areas assigned to the Palestinians by international law.

This position runs counter to that of the United Nations, which claims Israel’s settlements in occupied Palestinian territory have “no legal validity”, and “constitute flagrant violation of international law”.

In their new legislation, members of Congress claim the UN is considering a resolution to withhold assistance from – and prevent trade with – settlements in East Jerusalem, the West Bank, and the Golan Heights.

The Israel Anti-Boycott act would punish any American who supported such measures.

However, the American Civil Liberties Union (ACLU) has argued that the bill would “impose civil and criminal punishment on individuals solely because of their political beliefs about Israel and its policies”, in a letter sent to members of the Senate.

“In short, the bill would punish businesses and individuals solely based on their point of view,” it wrote. “Such a penalty is in direct violation of the First Amendment.”

Israel: From independence to intifada Show all 7 1 /7 Israel: From independence to intifada Israel: From independence to intifada The proclamation of the state of Israel is read by David Ben-Gurion in Tel Aviv on 14 May 1948 © EPA Israel: From independence to intifada Sixty years on, an illuminated flag is shown in Tel Aviv this week © PA Israel: From independence to intifada Young Jews celebrate the proclamation of the state of Israel in 1948 © AFP/Getty Images Israel: From independence to intifada Palestinian children throw stones at a retreating Israeli tank during an incursion into the West Bank city of Jenin in August 2003 following a suicide bombing in Jerusalem © AP Israel: From independence to intifada How Israel's borders have changed - click image to enlarge © Independent Graphics Israel: From independence to intifada From 1948-50, the world's mostcelebrated war photographer Robert Capa captured extraordinary imagesof Israel's pioneering settlers. Here, Turkish immigrants arrive in Haifa © Robert Capa/Getty Images Robert Capa/Magnum Israel: From independence to intifada The Negba kibbutz, where the walls have been damaged by shells fired during the Israeli-Arab war © Robert Capa/Getty Images Robert Capa/Magnum

Still, the bill – reportedly drafted with the help of the American Israel Public Affairs Committee (AIPAC) – has received widespread bipartisan support.

Even liberal-leaning senators like Kirsten Gillibrand of New York and Maria Cantwell of Washington, and representatives like Adam Schiff of Massachusetts, have signed on to the legislation.

Conservatives like Senators Ted Cruz of Texas and Marco Rubio of Florida also support it.

When asked by The Intercept about this support, many legislators seemed unfamiliar with the details.

Democratic Senator Gary Peters of Michigan responded by asking: “What’s the Act?”

Senator Claire McCaskill claimed she had not read the ACLU letter, but would “take their position into consideration, just like I take everybody’s position into consideration”.

Meanwhile, Senator Benjamin Cardin – the bill’s primary sponsor – said that he “doesn’t think” the bill criminalises participating in boycotts, as the ACLU has claimed.