The Redstones, the family that controls Viacom Inc. and CBS Corp., have taken their private squabble public in a battle that throws into question succession plans for the global media company.

Viacom and CBS Executive Chairman Sumner Redstone fired the first volley when, in a letter posted on Friday at Forbes magazine's Web site, he slammed his daughter, Shari Redstone, for having made little or no contribution to the building of the conglomerate.

Shari Redstone, in response, suggested through a spokeswoman she would be willing to part with her stake -- valued at $1.6 billion.

The latest dispute comes after Shari Redstone, 52, pushed for executive compensation to be more closely tied to executive performance, according to a Fortune magazine article. The dispute also has raised questions on whether she would succeed her father without board approval after his death.

Sumner Redstone said he would be willing to buy out her stake -- as long as the price is acceptable -- in a letter to Forbes reporter Robert Lenzner.

Shari has no desire to be 'bought out' of National, a spokeswoman fired back in an e-mailed statement. National is an entity that controls 80 percent of CBS and Viacom, which split apart in 2006 to appeal to different classes of shareholders.

If Sumner wishes to settle matters that way, Shari will consider a resolution that fairly reflects her 20% ownership of National, which has been publicly valued at $8 billion, the spokeswoman added.

News of a falling out between father and daughter had sent shares of Viacom up more than 3 percent on Thursday as speculation revived that Viacom or CBS might be sold off. Viacom shares gave up much of those gains on Friday.

A Viacom spokeswoman declined comment.

Viacom has said speculation that it was up for sale was wrong. But Sumner Redstone's letter suggested the opposite, one analyst said.

The direction it's heading now could make it more likely that Viacom could eventually get sold, David Joyce, analyst at Miller Tabak, said. It's more likely assets will be sold.

The latest family feud throws into question succession plans at Viacom and CBS, a recurring theme in Sumner Redstone's business. He has forced out two chief executives, Frank Biondi and Mel Karmazin.

Sumner Redstone also settled a lawsuit filed by estranged son, Brent Redstone, in a dispute over Brent's share of the family fortune.

Shari Redstone was appointed vice chairman of both companies following the ouster of former Viacom CEO Karmazin in 2005 and was seen as her father's eventual successor.

Until recently Sumner touted Shari's achievements at CBS and Viacom, praising her 'major role' there and describing her as 'great business woman' with 'no weaknesses,' Shari Redstone's spokeswoman said.

She owns an estimated 16 percent of each company and 20 percent of National Amusements, which controls about 80 percent of the voting stocks of Viacom and CBS.

In the letter, Redstone reiterated his position that his successor will be chosen by the boards of Viacom and CBS Corp., in accordance with proper corporate governance.

While my daughter talks of good governance, she apparently ignores the cardinal rule of good governance that the boards of the two public companies, Viacom and CBS, should select my successor, Redstone wrote.

Shari Redstone's spokesman said, It is unfortunate that Sumner has chosen to publicize what Shari had hoped would remain a private family matter.

Viacom