U.S. Senator Elizabeth Warren of Massachusetts, one of the leading progressive voices within the Democratic Party, said on Monday that she opposes the controversial Israel Anti-Boycott Act. Civil rights groups have warned that the bill could hurt free speech by imposing penalties on U.S. citizens for supporting boycotts of Israel and the settlements.

The bill was cosponsored by a bipartisan group of senators and members of the House of Representatives, but criticism from the American Civil Liberties Union has caused a number of senior Democrats to announce they will reconsider their support for it, including Massachusetts Democratic Representative Joe Kennedy.

One of the main reasons the ACLU has come out strongly against the bill is that violating it could lead to a minimum civil penalty of $250,000 and a maximum one of $1 million, or a lengthy period in jail. The ACLU pointed to First Amendment protections in their criticism, noting that the bill "cannot be fairly characterized as an anti-discrimination bill."

One senator – Democrat Kirsten Gillibrand of New York - withdrew her cosponsorship earlier this week, stating that she supports the bill's main objective of fighting BDS but would only support the bill if its language was changed to avoid legal ambiguity. Gillibrand's move made her the most senior Democratic politician to demand the AIPAC supported bill be changed.