Is Fox facing a blackout on iCloud and UltraViolet?

And then there was one.

With Universal reaching an agreement with HBO to relax contract rules limiting cloud-based distribution of movies during their pay-TV window, Fox is now the only studio that faces restrictions for its titles on Apple’s iCloud and UltraViolet.

Fox and HBO are still working on an adjustment to their long-term agreement that would allow digital storage and access of Fox titles on these cloud services during their pay TV window. Access generally starts six months after DVD release and extends anywhere from 12-18 months. (Depending on the deal and the movie, films can also later re-enter second and third pay TV windows.)

But the clock is ticking. On Monday, Walmart will launch a retail promotion campaign designed to kickstart the struggling UltraViolet cloud initiative — and all the studios were supposed to be aboard. (Update: Disney is not in the consortium backing UltraViolet, a fact not mentioned in this report earlier.)

That’s when Hollywood’s major studios will make about 4,000 titles available for UltraViolet storage. But Fox’s 10-year, $1 billion pay TV deal with HBO, signed in 2007, will limit its participation in UltraViolet. The studio-backed initiative offers DVD and Blu-ray purchasers a cloud-based digital copy of the movie they just bought, as well as films they already have in their disc library.

Those who purchase Fox movies like Rise of the Planet of the Apes on iTunes will be similarly affected, with access to iCloud restricted (see lower left hand corner of the embedded photo). Put simply, when Fox movies enter their various pay TV windows, they will be blacked out from the cloud.

Last year, Warner Bros., which like HBO, is also owned by Time Warner, worked out an adjustment to its HBO contract whereby consumers who purchased the studio’s films prior to their entry into the pay TV window could still access and store their bounty in iCloud and UltraViolet during the blackout period.

On Monday, paidContent confirmed a Mac Rumors report that Universal was able to get HBO to agree to a similar allowance.