President Obama on Friday vetoed legislation that would allow families of 9/11 victims to sue Saudi Arabia in U.S courts, setting up a high-stakes showdown with Congress.

“I recognize that there is nothing that could ever erase the grief the 9/11 families have endured," Obama wrote in his veto message. "Enacting JASTA into law, however would neither protect Americans from terrorist attacks nor improve the effectiveness of our response to such attacks."

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Obama’s move opens up the possibility that lawmakers could override his veto for the first time with a two-thirds vote in both chambers.

Republican and Democratic leaders have said they are committed to holding an override vote, and the bill’s drafters say they have the support to force the bill to become law.

The Justice Against Sponsors of Terrorism Act (JASTA) unanimously passed through both chambers by voice vote.

But the timing of the president’s veto is designed to erode congressional support for the bill and put off a politically damaging override vote until after the November elections.

Obama waited until the very end of the 10-day period he had to issue a veto, hoping to buy time to lobby members of Congress against the measure.

White House officials also hope congressional leaders will leave Washington to hit the campaign trail before trying for an override, kicking a vote to the lame-duck session after the election.

But Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellGraham: GOP will confirm Trump's Supreme Court nominee before the election Trump puts Supreme Court fight at center of Ohio rally The Memo: Dems face balancing act on SCOTUS fight MORE (R-Ky.) has said the upper chamber will remain in session until the veto override vote is done.

“Now that we have received the veto message from the president, the Senate will consider it as soon as practicable in this work period,” said David Popp, a McConnell spokesman.

Under current law, 9/11 victims' families may sue a country designated as a state sponsor of terrorism, such as Iran. JASTA would allow U.S. citizens to sue countries without that designation, including Saudi Arabia.

The measure has touched a political nerve ahead of an election in which terrorism has emerged as a central issue. It has strong bipartisan support and is backed by 9/11 families’ organizations.

Those families have sought damages from Saudi Arabia, since 15 of the 19 hijackers on Sept. 11, 2001 hailed from that country.

Critics have long been accused the Saudi government of directly or indirectly supporting the attacks, though a concrete link has never been proven.

In a statement, the 9/11 Families & Survivors United for Justice Against Terrorism said they are "outraged and dismayed" by the veto and call his reasoning "unconvincing and unsupportable."

"No matter how much the Saudi lobbying and propaganda machine may argue otherwise, JASTA is a narrowly drawn statute that restores longstanding legal principles that have enjoyed bipartisan support for decades. It will deter terrorism and hold accountable those nations that support and fund it," the statement read.

Obama has long strongly opposed the legislation, arguing it would undermine sovereign immunity and open up U.S. diplomats and military service members to legal action overseas if foreign countries pass reciprocal laws.

He echoed those concerns in his Friday veto message and said the law could complicate U.S. relationships with its allies and international cooperation.

"JASTA threatens to reduce effectiveness of our response to state involvement in terrorism by taking such matters out of the hands of national security and foreign policy and putting them in the hands of courts and private litigants," Obama wrote.

He also said "JASTA would upset longstanding international principles regarding sovereign immunity, putting in place rules that, if applied globally, could have serious implications for U.S. national interests."

The administration has been wary of angering Saudi Arabia, which is forcefully lobbying against the measure, especially after Obama brokered the nuclear deal with Iran that was seen by Riyadh as a challenge to the U.S.-Saudi alliance.

Similar concerns have been voiced by members of Congress in both parties following the bill’s passage, and the White House hopes that leads lawmakers to abandon the measure.

But leading Democrats like Sen. Charles Schumer Chuck SchumerJacobin editor: Primarying Schumer would force him to fight Trump's SCOTUS nominee CNN's Toobin: Democrats are 'wimps' who won't 'have the guts' to add Supreme Court seats Republican senator says plans to confirm justice before election 'completely consistent with the precedent' MORE (D-N.Y.) and House Minority Leader Nancy Pelosi (D-Calif.) have said they will buck the president and support overriding his veto.

“This is a disappointing decision that will be swiftly and soundly overturned in Congress," Schumer said in a statement. "I believe both parties will come together next week to make JASTA the law of the land."

- Updated at 4:34 p.m.