A two-thirds vote is needed in each chamber for the bill to become law without Trump's signature.
President Donald Trump on Sunday tweeted that he intends to veto a wide-ranging defence policy bill, raising new but unspecified concerns about China as a reason to reject a traditionally bipartisan measure with a nearly 60-year track record of being signed into law.
“The biggest winner of our new defence bill is China! I will veto!” Trump said.
The White House did not immediately respond to an emailed request for comment on Trump's specific concerns about China.
Senate Majority Leader Mitch McConnell, R-Ky., has said the bill would help deter Chinese aggression. Other GOP backers of the measure, including Sen. John Thune of South Dakota, the second-ranking Senate leader, and Rep. Mike Gallagher of Wisconsin, a member of the House Armed Services Committee, have tweeted that the bill would deter threats from countries such as China.
The threat was Trump's first since the defence bill cleared the Senate on Friday, following earlier passage by the House. Both chambers approved the measure by margins large enough to override a veto, which would be a first for Trump and would come not long before he leaves office Jan 20.
A two-thirds vote is needed in each chamber for the bill to become law without Trump's signature.
Trump, however, has a history of failing to follow through on action he has threatened.
The president has made numerous threats over Twitter to veto the bill over a requirement that military bases honouring Confederate leaders eventually be renamed. He also threatened a veto to try to force lawmakers to include provisions — unrelated to the military and national defence — to punish social media companies he claims were biased against him during the election.
Congress has approved the bill, known as the National Defense Authorization Act, for nearly 60 years in a row. The current version affirms 3% pay raises for U.S. troops and authorizes more than $740 billion in military programs and construction.
The measure guides Pentagon policy and cements decisions about troop levels, new weapons systems and military readiness, military personnel policy and other military goals. Many programs can only go into effect if the bill is approved, including military construction.
McConnell, in a rare break with Trump, had urged passage despite Trump's threat to veto it. McConnell said it was important for Congress to continue its nearly six-decade-long streak of passing the defence policy bill.
In addition to the budget and pay raises it would provide, McConnell said the bill will “keep our forces ready to deter China and stand strong in the Indo-Pacific.”
Gallagher tweeted last week that the United States was at the beginning of a “New Cold War” with China and that the defence bill “takes important steps to help us meet these challenges and ultimately win this competition.”