AT&T has "approached" DirecTV about buying the satellite television company, according to the Wall Street Journal's sources.

DirecTV has 20.25 million subscribers in the US (and another 17.6 million in Latin America), while AT&T has 5.7 million U-verse TV subscribers.

"The nearly 26 million subscribers served by the combined company would compare with Comcast which—with TWC—would serve close to 30 million subscribers," the Journal wrote. Comcast has 21.7 million cable TV customers today but is trying to buy Time Warner Cable.

Buying DirecTV would probably require AT&T to spend at least $40 billion. AT&T approached DirecTV about an acquisition after Comcast announced its deal to buy TWC, the Journal wrote: "It is unclear whether the companies are in detailed talks, but another person familiar with the situation said that DirecTV would be open to a deal. The satellite TV industry is facing a slowdown in subscriber growth after years of adding customers. The pay television market in the US is now mature, with about 90 percent of US households with TV now subscribing to either cable, satellite, or phone company-delivered television."

In recent years AT&T also held talks with Dish Network, which has 14 million customers and has remained independent. There have recently been reports that Dish and DirecTV are talking about merging.

An AT&T purchase of DirecTV would face regulatory scrutiny from the Justice Department and Federal Communications Commission. "Observers say the deal would be more likely to gain approval if the combined company can show it would provide competition for Comcast and other cable companies in the high-speed broadband market," the Journal wrote. "A source familiar with antitrust reviews said regulators would likely be concerned about the impact on markets where AT&T already offers high-speed broadband access and pay-TV via its U-Verse project. AT&T may be required to divest DirecTV subscribers in such markets."