CBS and Viacom have gone from corporate siblings to competitors. A new channel being launched by Viacom, in conjunction with two movie distributors, will compete with pay channels like CBS’s Showtime and Time Warner’s HBO and lead to a smaller till of movies for them to premiere.

The new network, announced yesterday by the three partners in the project, is the first premium movie network to launch in years, but more importantly, the venture represents a bid by the studios to cut out the middleman in bringing their films to cable.

Lead investor Viacom, Lions Gate Entertainment and Metro-Goldwyn-Mayer Studios will launch the as-yet untitled network in fall 2009.

The lineup will include original series and feature films made by the five studios under their umbrella.

That means that Showtime, HBO and Starz will not have the chance to premiere future films from the companies, like the highly anticipated summer release “The Love Guru” with Mike Myers, which will air on the new channel.

It also further heats up the growing rivalry between Viacom and CBS, which were part of the same Viacom company until Sumner Redstone split them up several years ago.

“I have stated from the beginning that Viacom and CBS have the right to pursue their own strategic objectives in the best interest of their individual shareholders. Competition between the two companies hones their skills and their productivity,” said a statement released yesterday by Redstone, who remains chairman of CBS and Viacom.

Recently CBS said it would get into the feature film business, competing with Viacom’s Paramount Pictures and MTV Pictures. Showtime is also going after the hip young people who watch many of Viacom’s channels, such as Comedy Central, Spike and MTV, with edgy, sex-soaked original series such as “The Tudors” and “Californication.”

Showtime has insisted that its original series are the key to its future, and it looks like that claim will be tested. With the new network launching, Showtime also loses a number of prominent movies.

The network has had agreements with each of the three companies to show their new movies first, but its contract with Viacom included only movies that debuted through 2007, while pacts with MGM and Lions Gate run out at the end of this year after negotiations for a new deal with Showtime stalled.

Those three were the only companies that Showtime had exclusive deals with; HBO has deals with four major studios while Starz has partnered with Sony and Walt Disney.

That could lead to speculation that the announcement of the new channel is simply a tactic to force more favorable negotiation with Showtime, but the fact is that studios have been mulling a new direct-to-consumer approach for years, especially with all the new technology available.

One increasingly polarizing issue between pay channels and their studios has been exclusivity demands. For example, pay cable networks will often insist on restrictions on internet or on-demand offerings for new movies.

With these studios now controlling distribution of their films, expect to see more crossover between pay cable, on-demand and online.