WASHINGTON (Reuters) -Shares of U.S. Steel rose 5% on Monday, as a $14.9-billion bid for the well-known American firm from Nippon Steel ( NISTF ) approached the finish line and after details of the U.S. government's golden share emerged over the weekend.

U.S. Steel shares hit $54.86, just short of the $55 Nippon Steel ( NISTF ) offer, after the Trump administration gave a green light to the merger on Friday via an executive order and a signed agreement to assuage national security concerns, capping off a tumultuous 18-month effort.

But questions swirled about the "golden share" President Donald Trump had suggested gave the American people a 51% stake in the struggling U.S. firm as part of the acquisition.

"President Trump has secured a perpetual Golden Share as part of Nippon Steel's ( NISTF ) acquisition of U.S. Steel," Commerce Secretary Howard Lutnick posted on social media on Saturday.

He added the share would prevent the companies from reducing or delaying $14 billion in promised investments, transferring production or jobs outside the United States, or closing or idling plants before certain time frames, without the president's consent.

That power could be conferred via a single share of preferred stock, called Class G for "gold," a U.S. official said, confirming a report by the New York Times.

In a national security agreement term sheet proposed to the Committee on Foreign Investment in the U.S. in September 2024 and obtained by Reuters, Nippon Steel ( NISTF ) pledged that a majority of U.S. Steel's board members would be American, and that three of them - known as the "independent U.S. Directors" will be approved by CFIUS.

"U.S. Steel may reduce Production Capacity if and only if it is approved by a majority of the Independent U.S. Directors," the term sheet stated, adding that core U.S. managers will be U.S. citizens.