Open warfare appears on the verge of breaking out on the Open Cloud.

On Friday, Microsoft Corp. (MSFT) and Amazon.com Inc. (AMZN) accused a group of big technology companies of conspiring to unilaterally set the ground rules for cloud computing. Both companies are hoping to become big players in cloud computing, a growing field in which computer processing is handled at data centers and accessed by customers via the Internet.

The target of their umbrage is the Open Cloud Manifesto, a document drafted by big technology companies that calls for interoperability between the emerging cloud technologies and defines practices in the field. The manifesto has the support of dozens of household-name technology companies, which don't want to be named until the document is made public.

In a blog post, Steven Martin, a Microsoft developer, says the software giant was shown a copy of the manifesto and asked to sign it without modifications or offering input, something he says goes against the spirit of the document.

"We were admittedly disappointed by the lack of openness in the development of the cloud manifesto," Martin wrote. Martin says the standards for cloud computing should be defined through a process "that is open to public collaboration and scrutiny."

The brewing row between the camps could crimp adoption of cloud computing if potential customers, especially the big corporations whose data the cloud providers want to host, sense a standards war is in the offing. That, in turn, could disrupt what is widely seen as a potential driver of revenue growth for tech companies as they emerge from the recession.

Earlier this week, IT research firm Gartner forecast revenue from cloud services would grow 21.3% to $56.3 billion in 2009 and would reach $150 billion in 2013.

The manifesto says the full benefits of cloud computing, including pay-per-usage pricing, could be hampered if cloud companies don't share information, according to a blog posting by Reuven Cohen, founder of Toronto-based cloud computing technology provider Enomaly Inc., which was involved in drafting the document.

"The manifesto...speaks to the fundamental principles that the Internet was founded upon - an open platform available to all," Cohen said in the post. The manifesto is expected to be unveiled Monday, the blog said.

Cohen did not respond to an email seeking comment.

Analysts say adoption of a set of standards will help spur the growth of the cloud. Although some companies are experimenting with cloud computing, it is far from mainstream.

"We'd like to see more interoperability," said Stephen O'Grady, an analyst at IT research firm Red Monk. "At the moment moving between platforms isn't that easy."

So far, however, the move toward unity has been fractious.

"The best way to illustrate openness and customer flexibility is by what you actually provide and deliver for them," Amazon.com, one of the pioneers in cloud computing, said in a statement.

-By Jessica Hodgson, Dow Jones Newswires; 415-439-6455; jessica.hodgson@dowjones.com

(Scott Morrison contributed to this report.)