The acquisition was controversial as some argued foreign ownership over one of America’s largest steel producers posed a threat to national security. U.S. Steel (NYSE: X) stock was down more than 5% in midday trading Friday,

The companies condemned the president's decision and hinted at taking legal action, while U.S. Steel's CEO accused Biden of "political corruption."

US President Joe Biden has formally blocked the takeover of US Steel by a bigger Japanese company, saying foreign ownership could pose risks for national security. The controversial decision comes a year after Nippon Steel first announced the $14.9bn (£12bn) deal, describing it as a lifeline for its smaller Pennsylvania-based rival.