Early movers: YHOO, LMT, UAL, TMUS, AAPL, VRX, PCP, VZ, YUM & more

Traders work on the floor of the New York Stock Exchange.
Brendan McDermid | Reuters
Traders work on the floor of the New York Stock Exchange.

Check out which companies are making headlines before the bell:

Yahoo — Activist investor Starboard Value sent a letter to the Yahoo board, saying it has lost confidence in the ability of the company's board and management to create shareholder value and that significant changes are needed. (Disclosure: CNBC has a content-sharing partnership with Yahoo's finance site.)

Oracle — Oracle was upgraded to "buy" from "hold" at Evercore, saying the risks faced by the software giant are already reflected in the stock's price and that the promise of recurring revenue growth is attractive.

Lockheed Martin — RBC upgraded the defense contractor's stock to "outperform" from "sector perform," helped by less government defense budget uncertainty.

Tyco International — RBC downgraded Tyco to "sector perform" from "outperform," saying cyclical factors make the fire and security protection company less attractive, even though the firm still likes Tyco's business model.

Delta, United Continental, Southwest, American Airlines Group — A new fare hike of up to $8 round-trip appears to be taking hold, with most of the major carriers instituting that increase.

Panera Bread — The restaurant chain said its chain-wide soup menu no longer contains artificial colors, flavors, sweeteners, or preservatives.

T-Mobile US — The wireless carrier said it added 8.3 million customers in 2015, its second consecutive year with subscriber additions above the 8 million mark.

SiriusXM — The satellite radio service announced it had added 2.3 million net subscribers during 2015. That was more than the two million the company had most recently forecast.

Yum Brands — Yum Executive Chairman and former CEO David Novak will retire in May. The restaurant operator will appoint a non-executive chairman from its board to replace Novak, with the announcement to come at its annual shareholder meeting.

Apple — Apple is under pressure once again following reports that it will cut production of the iPhone 6S and 6S Plus by about 30 percent during the current quarter.

General Motors — The automaker announced a 5.2 percent increase in China sales for 2015. GM and its China joint venture partners sold a total of 3.61 million vehicles during the year.

Valeant Pharmaceuticals — The drug maker will reportedly appoint an interim chief executive officer to fill the shoes of Michael Pearson, who is currently hospitalized with pneumonia. Dow Jones reported it is not clear whether the person appointed would temporarily or permanently replace Pearson.

Verizon — Verizon has begun an auction to sell its data centers, according to Reuters. Citigroup is said to be advising Verizon on the possible sale, which the company hopes will garner more than $2.5 billion.

Sonic — Sonic reported quarterly profit of 24 cents per share, 1 cent above estimates, with the restaurant operator's revenue also exceeding Street forecasts. Same-restaurant sales were higher by 5.3 percent compared to a year earlier.

Precision Castparts — The European Commission approved the acquisition of the aerospace company by Berkshire Hathaway, saying the deal did not raise competition concerns.