President Donald Trump has vetoed an annual defense bill authorizing billions of dollars in military spending after complaints that the bill did not include changes to Section 230, the provision that gives social media companies legal immunity over much of the content posted by their users.

Earlier this month, Trump threatened to veto the $740 billion spending bill, the National Defense Authorization Act, unless Congress included a provision that would repeal Section 230 of the Communications Decency Act. Congress approved the measure by veto-proof margins in December. House lawmakers will return to Capitol Hill on Monday for a vote to override the president’s veto, according to Politico’s Connor O’Brien.

“Section 230 facilitates the spread of foreign disinformation online, which is a serious threat to our national security,” Trump said in a statement Wednesday. “It must be repealed.”

Amending or repealing Section 230 has become a priority for the Trump administration over the last few months. In May, Trump signed an executive order urging the Federal Communications Commission to reinterpret the law. The order came in response to Twitter fact-checking a tweet from Trump for the first time, over false claims made on voter fraud. That pressure has only grown in the wake of the election, as President Trump has continued to use social platforms to promote false evidence of fraudulent voting.

Social media companies like Facebook and Twitter have been under immense pressure to moderate the president’s tweets when he posts falsehoods online. The companies’ increasing moderation efforts have led Trump and Republican lawmakers to make misleading claims that the platforms are biased against conservatives. 

In a statement, Trump said that Congress’ “failure to terminate the very dangerous national security risk of Section 230 will make our intelligence virtually impossible to conduct without everyone knowing what we are doing at every step.”

Previously, lawmakers had been broadly skeptical of efforts to pass 230 reform as part of the defense bill — but some Senate Republicans now say they will not vote to override Trump’s veto. “I will not vote to override presidential veto unless effort is made to wind down Section 230,” Sen. Lindsey Graham (R-SC) said in a statement Wednesday. In a counterpoint to Graham, Senate Armed Services Committee Chairman Jim Inhofe (R-OK) said he supports changing Section 230 as policy, but will vote in opposition to the president once the motion is brought to the floor.