Republican and Democratic lawmakers say the wide-ranging defense policy bill, which the Senate sent to the president on Friday, would be tough on China and must become law as soon as possible.
Both the House and Senate passed the measure by margins large enough to override a potential veto from the president, who has a history of failing to carry out actions he has threatened.
"The biggest winner of our new defense bill is China! I will veto!" Trump said in a new tweet.
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 counter threats from countries such as China.
Sen. Jack Reed of Rhode Island, the top Democrat on the Senate Armed Services Committee, said Trump's declaration that China is the biggest winner in the defense bill is false. Reed also noted the shifting explanations Trump has given for the veto threats.
"President Trump clearly hasn't read the bill, nor does he understand what's in it," Reed said. "There are several bipartisan provisions in here that get tougher on China than the Trump Administration has ever been."