Dish Network Chairman Charlie Ergen recently contacted DirecTV Chief Executive Officer Mike White to discuss a merger of the two satellite television companies, according to several people with knowledge of the matter. Shares of both companies rose. Ergen made the approach in response to Comcast Corp.’s $45 billion acquisition of Time Warner Cable announced in mid-February, one of the people said, asking not to be identified discussing confidential information. White is reluctant to push forward with formal talks out of concern regulators may block the deal because the two companies directly compete with each other, another person said. DirecTV is the largest U.S. satellite-television operator, with about 20 million paying subscribers. Dish is No. 2 with about 14 million subscribers, and also has a spectrum portfolio that may be valued at almost $26 billion, according to Bloomberg Industries.