Check out the companies making headlines before the bell:
Union Pacific — Shares of the freight-hauling railroad rose more than 7.5 percent in premarket trading after it hired a new chief operating officer. The Omaha, Nebraska-based railroad said Monday that it hired longtime Canadian National railroad executive Jim Vena as COO. Vena will take the reins on January 14. Seaport Global Securities upgraded the stock to a "buy" rating following the news.
Nordstrom — The department store's stock rose 1.6 percent before the bell after Morgan Stanley upgraded shares on Monday. Analyst Kimberly Greenberger said catalysts such as the opening of its flagship New York City Women's store in fall 2019 as well as underperformance in 2018 make the stock slightly more attractive based from a valuation perspective.
Monster Beverage — The energy drink company rose 2.9 percent in premarket trading Tuesday after SunTrust analyst William Chappell told clients that he thinks the concerns around rival Coca-Cola launching a competitive energy drink products are "overblown." He also wrote that Monster Beverage's gross margins are too low given recent input cost declines and the apparently successful implementation of U.S. price increases.
Mastercard — The stock dropped 0.6 percent before the bell after Bank of America/Merrill Lynch downgraded it to "neutral" from "buy." Analyst Jason Kupferberg highlighted near-term concerns regarding cross-border deceleration and fiscal 2019 estimates, which he said "look high especially on revenue."
PG&E — The beleaguered utility company was set to drop another 3.4 percent on Tuesday. The California company is set to face at least $30 billion in liability for fire in 2017 and 2018, sources told CNBC's David Faber on Monday, reigniting concerns that it could face capital and liquidity constraints. It's considering bankruptcy protection for some or all of its business as it faces a big fourth-quarter charge related to liability for the fatal fires, Reuters reported Friday.
PPG — The stock slid more than 4.5 percent before Wall Street's opening bell despite reassurances from PPG Chairman Michael McGarry that its acquisition of a German automotive coatings company "is another step forward in our strategic growth plan that will provide further value to our customers and shareholders." The company said Monday it reached an agreement to buy Hemmelrath.
Samsung Electronics — The company issued guidance on Tuesday that its fourth-quarter earnings will likely sink thanks to tepid demand in its memory business. The South Korean tech giant said it sees operating profit for the three months ended December at 10.8 trillion Korean won ($9.67 billion), or 28.71 percent below a year ago. The figure missed market expectations, coming in 18.18 percent less than the 13.2 trillion won that analysts had predicted.
—CNBC's Saheli Roy Choudhury contributed reporting.