WASHINGTON (Reuters) -Nippon Steel ( NISTF ) plans to invest $14 billion in U.S. Steel's operations including up to $4 billion in a new steel mill if the Trump administration green lights its bid for the iconic U.S. company, according to a document and two people familiar with the matter.

Under details of the plan included in the document, the company will plow $11 billion into U.S. Steel's infrastructure through 2028. That includes $1 billion in a green field site, which is expected to grow by $3 billion over the following years and has not been previously reported. The total investment figure was previously reported by CTFN.

The super-charged investment pledge, up from an initial $1.4 billion, was pitched as part of a last ditch effort to win approval of the merger, which has drawn fire from both Presidents Donald Trump and Joe Biden.

The companies face a May 21 deadline for the completion of a fresh national security review of their proposed tie-up, which was blocked by Biden on national security grounds in January following a prior review. Trump would then have 15 days to decide the fate of the transaction, although the timeline could slip.

It is unclear if the billions in new investment will be enough to sway Trump. But the offer shows the lengths Nippon Steel ( NISTF ) is willing to go to to secure approval, with a looming $565 million breakup fee and current steep U.S. steel tariffs of 25% to access thriving American steel markets.

U.S. Steel declined to comment. Nippon Steel ( NISTF ), the White House and the Treasury Department, which leads the committee overseeing the national security review, did not immediately respond to requests for comment.