Apple's case against a Macintosh clone vendor took a new twist this week when defendant Psystar accused the company of violating anti-trust laws.

For several months, Psystar has sold systems pre-installed with Apple's OS X operating system. The company uses open source tools to allow the MacOS to run on PC hardware. Psystar touts its products as a cheaper alternative which fills voids in Apple's product line, such as consumer tower models.

Apple filed suit against Psystar in July, accusing the company of copyright infringement and illegally distributing OS X in violation of the company's end-user license agreement. The end user licence agreement (EULA) expressly forbids the installation of OS X on computers not produced by Apple.

In retaliation, Psystar plans to put forth an antitrust case against Apple. The suit will reportedly claim that Apple is violating antitrust laws by bundling the operating system to its hardware.

Similar accusations were aimed at Microsoft when the company began bundling Internet Explorer with Windows. The case eventually lead to the company's epic antitrust showdown with US and European authorities.

If successful, the Psystar suit would open the door for the first legitimate Mac clones in more than a decade.

Shortly after his return to the company in the late 90's, Steve Jobs ended the licencing agreements the company held with several third-party manufacturers and restricted the installation of MacOS to Apple-branded computers.

Subsequent Macintosh sales helped pull the company out of its financial troubles, and the Mac has now become Apple's biggest source of revenue.