The national security agreement between President Donald Trump, Nippon Steel Corp., and US Steel to merge the two companies opens the door to unprecedented control by the president over the steelmaker’s operations and its relations with the workers’ union.

Nippon Steel's $14.9-billion acquisition of U.S. Steel closed on Wednesday, the companies said, confirming an unusual degree of power for President Donald Trump after the Japanese company's 18-month struggle to close the purchase.

Nippon Steel completes its purchase of U.S. Steel after more than a year and half of high-stakes negotiations and national security concerns.