Despite a steady stream of meetings and calls with U.S. officials, and three revamped proposals to assuage national security concerns, Nippon Steel has failed to garner approval from a powerful panel reviewing its $14.9 billion bid for U.S. Steel, a letter shows.

The letter, sent Saturday, sets the stage for U.S. President Joe Biden, who has long opposed the deal, to block it. The Committee on Foreign Investment in the United States (CFIUS), which reviews deals for national security risks, has a Dec. 23 deadline to approve the deal, extend the review, or recommend Biden scuttle it.

If the agencies that make up the panel remain at loggerheads, as the letter states, they will refer the matter to Biden to take action.