Families who lost loved ones in the Sept. 11 attacks are calling on President Barack Obama to sign a controversial piece of legislation.

Survivors and widows staged a protest outside the White House on Tuesday and held a news conference on Capitol Hill. The president has threatened to veto the Justice Against Sponsors of Terrorism Act.

The bill would allow U.S. victims of terror attacks and their families to sue foreign actors who support terrorism. It passed both the House and Senate unanimously, and supporters said it’s about justice.

“We’d like President Obama to sign a clear message across the world,” said Mindy Kleinberg, a 9/11 widow. “If you’re going to come to our country and murder our citizens, we’re going to hold you accountable.”

The White House opposes the legislation, saying it will open up Americans to similar suits in different countries and damage diplomatic relations.