Apple may be forced to delay the launch of its long awaited next generation operating system because of impending legal action over its name - OS9.

A lawsuit has been filed against the company by US based firm Microware, which has held the trademark OS-9 for its own operating system since 1980.

Microware chief financial officer George Leonard confirmed that the suit had been filed, but said he was unable to comment further.

US court officials at Southern Iowa district court told VNU Newswire that the case was filed against Apple at the end of last week and that, as yet, it had had no response from Apple, which has 20 days to respond from the date of the filing.

According to trademark lawyers in both the UK and US, Microware has a very strong case and could apply to the courts for an injunction preventing the launch of Apple's OS9, due next month.

John Ottaviani, partner with US law firm Edwards & Angell, said Microware could have a good case against Apple.

"Microware has to prove whether there is a likelihood of confusion over the two marks. If both operating systems are for the same sort of use then certainly Microware has a claim and maybe a very good one," he said.

He added that Microware could ask the courts to stop the launch, for which it would need to pay a bond.

"It may just say to Apple, go ahead with the launch and run the risk. If Apple does then every product it sells will increase the amount it will need to pay to Microware should they win the case," he said.

"Apple is not like Microsoft," he added, "It is not big enough that a judgement against it like this wouldn't hurt."

Any delay would be a major blow to Apple, which has been trumpeting the features of this new OS for more than a year.

Only last month interim chief executive Steve Jobs told US newspapers that OS9 was "a whole new upgrade to the Macintosh operating system that's rolling out this Ocotober for $99...I think OS9 is going to be a really good release for us."

OS9, codenamed Sonata, is an interim update to the Mac operating system before OSX (pronounced OS ten) comes out next year. It is expected to have greater integration with the Internet, improved support for multiple users and an upgrade to its built-in search engine.

UK trademark experts said the case had merit and that Apple would have a battle on its hands, or possibly have to settle out of court to pay Microware a royalty fee for every copy of OS9 sold.

According to documents from the US Patent and Trademark office, seen by VNU Newswire, OS-9 was registered by Microware in April 1980, as a "computer operating program".

One US insider said he believed Steve Jobs had at one time planned to skip straight from OS8 to OSX, without clarifying why this might be. OSX is due next year and is a more significant revision of the Apple operating system.

Apple said it was unable to comment on pending litigation.