well as Texas Oil and Gas several years later. Recognizing its new scope, it reorganized its holdings as USX Corporation in 1986, with U.S. Steel (renamed USS, Inc.) as a major subsidiary. About 22,000 USX employees stopped work on August 1, 1986, after the United Steelworkers of America and the company could not agree on new employee contract terms. This was characterized by the company as a strike and by the union as a lockout. This resulted in most USX facilities becoming idle until February 1, 1987, seriously degrading the steel division's market share. A compromise was brokered and accepted by the union membership on January 31, 1987. On February 4, 1987, three days after the agreement had been reached to end the work stoppage, USX announced that four USX plants would remain closed permanently, eliminating about 3,500 union jobs. The closure of so many plants created the term "rust belt" for a region of idle and derelict factories. Corporate raider Carl Icahn launched a hostile takeover of the steel giant in late 1986 in the midst of the work stoppage. He conducted separate negotiations with the union and with management and proceeded to have proxy battles with shareholders and management. But he abandoned all efforts to buy out the company on January 8, 1987, a few weeks before union employees returned to work. Recent history At the end of the twentieth century, the corporation was deriving much of its revenue and net income from its energy operations. Led by CEO Thomas Usher, U.S. Steel spun off Marathon and other non-steel assets (except railroad company Transtar) in October 2001. It expanded internationally for the first time by purchasing operations in Slovakia and Serbia. In the early 2010s, U.S. Steel began investing to upgrade software programs throughout their manufacturing facilities. In January 2012, U.S. Steel sold its Serbian mills outside Belgrade to the Serbian government, as their operations had been running at an economic loss. On May 2, 2014, U.S. Steel announced an undisclosed number of layoffs affecting employees worldwide. On July 2, 2014, U.S. Steel was removed from S&P 500 index and placed in the S&P MidCap 400 Index, in light of its declining market capitalization. In October 2019, U.S. Steel announced a $700 million investment in Big River Steel, which became the first steel facility to be LEED-certified in 2017, in exchange for a 49.9% ownership interest. In December