Sun faces "irreparable harm" if an injunction ordering Microsoft to include Sun's Java Runtime Environment (JRE) with its products is overturned, Sun said in a legal brief filed Friday.

The brief is the latest action in a private antitrust lawsuit filed by Sun against Microsoft in March 2002 regarding the emergence of Microsoft's .Net platform as a competitor to the Java language and JRE.

Sun alleges that Microsoft has tried to kill developer interest in Java by distributing its own version that is incompatible with the version of Java controlled by Sun, thus creating uncertainty in the developer community and driving developers to use Microsoft's competing .Net platform.

Sun asked for, and on December 23, 2002, was granted an injunction that ordered Microsoft to offer the JRE with all versions of Windows XP and with all Web browsers that include .Net functionality. Microsoft appealed the decision, and the injunction was halted in January by an appeals court pending review.

Microsoft originally asked the court to set aside the injunction, saying that Java, and not .Net, was the dominant product in the market for distributed computing platforms.

Sun replies that the injunction must be granted before Microsoft's anti-competitive actions begin to tip the market towards .Net.

"Microsoft asks this court to wait until the harm to Sun and Java has become certain, at which point it will be irremediable and intervention will be pointless," Sun wrote, adding, "The harm confronting Sun is so egregious and irremediable, equity demands judicial intervention."

Sun has stated that Microsoft's action in offering its own incompatible Microsoft Java Virtual Machine (MSJVM) is a breach of Sun's copyright and an attempt to damage the Java platform. Microsoft now offers a Windows XP Service Pack, known as XP SP1a, which is identical to the previous service pack but excludes the MSJVM.

"Because Sun has established a prima facie claim of copyright infringement, it is entitled to both the presumption of probable success on the merits of its copyright claim and the presumption of irreparable harm if infringing conduct is not enjoined," Sun wrote.

Oral arguments in the case are scheduled for April 3.