By Stephen M. Silverman
Updated March 11, 2003 01:00 PM

The battle between “The Sopranos” star James Gandolfini and his network, HBO, is expected to get nastier on Tuesday, as the pay-cable network plans to countersue the actor, claiming he would cost the network $100 million by failing to show up for the fifth season of the popular — and highly profitable — Mob series, reports Variety.

“We are exposing the frivolous nature of (Gandolfini’s) claims in our answer and cross-complaint,” said attorney Bert Fields, who represents HBO (which, like PEOPLE, is part of AOL Time Warner).

Last week, Gandolfini sued HBO, claiming the network violated his contract by not properly notifying him of plans for a fifth season. This weekend, HBO chairman Chris Albrecht told The New York Times he was stunned by Gandolfini’s action, adding, “I can certainly see a scenario where this threatens the future of the series.”

“If he doesn’t show up by March 24, he’s going to owe a huge amount of money,” said Fields, who also said there are no plans to continue the show without Gandolfini.

On Sunday night, the actor won the Screen Actors Guild Award for his performance as the conflicted New Jersey crime boss.

“Maybe there’s some stuff lately that makes me seem ungrateful,” Gandolfini, 41, said during his acceptance speech, “but HBO — I’d like to thank you for what you’ve done … it is a great place to work.”

Gandolfini’s attorney, Marty Singer, told Variety, “We haven’t said he’s not going to show up. We’re waiting for information about the viability of our claim that he didn’t get proper notice. I would think HBO would want to give us that information rather than bring a lawsuit.”