The CBS board is preparing for merger talks with Viacom, people familiar with situation said.

The long-anticipated talks between the two companies controlled by the Redstone family's National Amusements are expected to begin in mid-June, though discussions could begin even sooner, the sources said. Viacom CEO Robert Bakish would likely run the combined entity.

Though no talks have occurred, Shari Redstone, vice chairwoman of CBS and Viacom, has long been in favor of marrying the two as the former looks to bulk up its balance sheet. The added size would likely help CBS compete for National Football League broadcast rights against big technology companies like Amazon and Facebook.

National Amusements has twice tried but failed to combine the media companies. Should the tie-up ultimately occur, National Amusements would likely pivot to a second deal, people familiar with the matter told CNBC earlier this year.

Discovery Communications, for one, was interested in selling to CBS or a combined CBS-Viacom entity, two people familiar with the matter told CNBC in January. The company is also expected to continue talks to acquire premium entertainment network Starz from Lions Gate, CNBC reported last week.

CBS' search for scale comes as big media faces continued hikes to carriage fees, making it more difficult for them as viewers ditch cable and satellite TV subscriptions in favor of over-the-top and streaming options.