The Mac clone maker Psystar, sued by Apple Inc. last month, fired back today with a countersuit charging Apple with restraint of trade, unfair competition and other violations of antitrust law.

Psystar says it has filed paperwork with a San Francisco federal court answering Apple's July 3 lawsuit and replying with one of its own.

"We're alleging restraint of trade, among other things," said Colby Springer, one of three lawyers from the firm of Carr & Ferrell LLP representing Psystar, "We're going to let the court decide."

Springer said the countersuit accuses Apple of violating the Sherman Antitrust Act and the Clayton Antitrust Act, in particularly for tying its Mac OS X operating system to its own hardware in the end-user licensing agreement (EULA). Because the EULA bars users from installing the OS on non-Apple hardware, Springer said, it's unlawful restraint of trade.

"Apple makes a good operating system, we don't deny that," said Springer. "This is about bringing Leopard [Mac OS X 10.5] to the masses."

Rudy Pedraza, the president and co-founder of Psystar, said somewhat the same thing. "It's not that people don't want to use Mac OS X, but they're not open spending an exorbitant amount of money for something that's essentially generic hardware."

Psystar, which has sold Intel-based OpenComputer desktops starting at $555 since April, and OpenServ servers since June, was sued by Apple last month on the basis of the Mac OS X EULA. In the lawsuit, Apple charged Psystar with copyright and trademark infringement, breach of contract and unfair competition because the Florida firm preinstalled its operating system on systems.

One expert in intellectual property (IP) litigation said last month that an Apple victory would probably put Psystar out of business, since if victorious, Apple would demand Psystar recall the machines it's sold to customers. At the time, Carole Handler, a partner in the IP department of Wildman, Harrold, Allen & Dixon, predicted Psystar would play the antitrust card.

In an interview earlier this month, Springer hinted that Carr & Ferrell's defense would include antitrust elements.

Today, Springer denied reports that Psystar was pirating or modifying Apple's software. "Every single copy of the OS is a purchased copy," said Springer. "Despite the allegations that there's a'master disc,' that's not the case. And allegations that Psystar has somehow modified [Mac OS X's] code to run on non-Apple systems, that's also not the case.

"There is no modification of any proprietary code of Apple's," Springer claimed. Psystar, however, has modified some of the open-source code that ships with Mac OS X, Springer acknowledged, but maintained that any modifications were under the licenses of each open-source component.

Pedraza, who spoke publicly about the case for the first time, echoed Springer. "We purchase copies of Mac OS directly from Apple or from an Apple authorized dealer," he said.

When asked if the countersuit cited any specific precedent in Psystar's favor, Springer responded: "No specific precedent, but we wouldn't be filing this if we didn't believe we could support it."

Psystar's countersuit asked for unspecified damages, which, if the case reaches trial, would be set there, Springer said. "We're not trying to shut down Apple," he said. "What we want to do is provide an alternative to Apple's hardware."

Apple already faces antitrust charges in a lawsuit first filed in 2006 over tight links between the iTunes music store to iPod players. That case, which is seeking class-action status, is similar to Psystar's, said Springer, in that both allege illegal tying.

Pedraza also said that Psystar was working on a mobile system able to run Mac OS X, although he declined to provide details of the potential notebook.

Apple officials did not respond to a request for comment on the Psystar countersuit.