More than 40 US senators on both sides of the aisle are pushing to outlaw support for a boycott against Israel, drawing heat from the American Civil Liberties Union (ACLU) for posing a major threat to free speech, the Intercept reports.

An international boycott of Israel—backed by entities as disparate as the UN, Britain's largest lecturers' union, and a coalition of artists including Brian Eno—has garnered support in response to the country's thorny occupation of Palestine, a move it escalated by establishing Israeli settlements in disputed territory. A handful of US campaigns support the boycott, which runs directly counter to mainstream American policy on Israel: The country is a major US ally and trading partner, and has been for years.

A Senate bill introduced in March would criminalize supporting the boycott, slapping anyone who violates the would-be law's terms with a minimum civil fine of $250,000 and a maximum criminal punishment of up to $1 million and 20 years in prison. That means if consumers or businesses decide not to make transactions with Israel or Israeli companies because of their stance on the boycott, they could be fined or charged. Even simply asking for information about the boycott could serve as grounds for charges, according to the ACLU.

So far, leaders on both the right and left have signed their support to the bill. Minority Leader Chuck Schumer, Kirsten Gillibrand, and Ron Wyden all co-sponsored it, as did outspoken Republicans like Marco Rubio, Ted Cruz, and Ben Sasse. In total, 29 Republicans and 19 Democrats have signed on.

The ACLU condemned the bill in a letter to the Senate, arguing that the measure is "antithetical to free speech" and is "in direct violation of the First Amendment."

"This bill would impose civil and criminal punishment on individuals solely because of their political beliefs about Israel and its policies," the ACLU wrote. "[We] urge you to oppose the bill, whether in committee or on the floor, unless it has undergone significant revision to resolve its constitutional infirmities."

According to the Intercept, the House introduced a similar measure on the same day back in March, co-sponsored by 63 Democrats and 174 Republicans. Not a single Senator or Representative has sided with the ACLU and come out against the move.