The U.S. Senate unanimously approved the Justice Against Sponsors of Terrorism Act (JASTA), which would allow 9/11 victims and their families to sue Saudi Arabia. JASTA now must be voted on by the House of Representatives.
Currently, countries can't be sued for the actions of terrorists due to sovereign immunity. However, JASTA would remove this protection and allow people to sue Saudi Arabia for reparations.
Saudi Arabia strongly opposes JASTA, and has threatened to pull economic support if it passes. The U.S. Treasury owes Saudi Arabia $116.8 billion. The White House also opposes JASTA, believing that it puts Americans abroad at risk and that sovereign immunity should not be taken away. However, a presidential veto can be overridden by a 2/3 majority vote by the Senate - which they claim to have.
There is no concrete evidence that Saudi Arabia sponsored the terrorists responsible for 9/11, but there is classified evidence which is rumored to confirm their involvement. Obama is being urged to declassify it.