Shameless actress Emmy Rossum is locked in a pay standoff that is holding up a possible eighth season of the popular Showtime dramedy.

Rossum, 30, who stars as the young Gallagher family matriarch Fiona on the hit series, not only is seeking salary parity with co-star William H. Macy, multiple sources tell The Hollywood Reporter she is taking the position she should be paid more per episode than Macy makes after years of earning much less than her Emmy-nominated co-star.

Macy, 66, who stars as drug and alcohol addict Frank Gallagher, recently renegotiated his deal with producer Warner Bros. Television for the yet-to-be announced eighth season and scored a raise that sources say puts his salary in the upper echelon of cable dramas. Now Rossum is seeking a similar deal — and to make more than Macy. The cast's last renegotiation a few years ago gave raises to all the main members of the ensemble. But Macy, who came into Shameless with an extensive film résumé and an Oscar nomination for his role in Fargo, always has been paid more than the rest of the cast.

Warner Bros. TV and Showtime declined comment.

It's worth noting that Shameless nearly has killed off Macy's Frank character, most recently wrapping season six with a cliffhanger in which he was thrown over a bridge into the Chicago River. (He survived.) On the flip side, Rossum's Fiona often has been the focal point of the series. Fiona, who is Frank's eldest daughter, is charged with overseeing the Gallagher household and her five siblings. Unlike in the British series on which the drama from producer John Wells is based, Fiona plays a key role in every episode. The U.K. Fiona (Anne-Marie Duff) has appeared as a regular only in seasons one and two and recurred in season 11. (The U.K. Frank, played by David Threlfall, has been a regular in all 11 seasons.)

In its seventh season, Shameless has become a key piece of Showtime's original scripted lineup. The drama has pulled off the rare feat of airing twice in the same calendar year (this year) in a bid to fill the originals gap created by Homeland's delay to early 2017. Shameless also is a key asset for Warner Bros. TV, which is attempting to sell more series to premium cable outlets as broadcast networks buy from their vertically aligned studios. But while the U.S. adaptation is a hit stateside, because it is based on a format it does not sell well internationally, limiting its value.

On the awards side, Macy has scored three best actor in a comedy series Emmy nominations, a Critics' Choice drama actor nom, a Golden Globe comedy actor nom, two SAG comedy actor noms and one win in the latter category. Awards season recognition can play a key role in salary renegotiations. Rossum, who was known for the feature films Phantom of the Opera and The Day After Tomorrow before breaking out in Shameless, has scored two Critics Choice best actress nominations for her work as Fiona. This season, Rossum made her directorial debut.

Sources say if Rossum closes her deal, producer WBTV then will renegotiate with the remainder of the cast, including Jeremy Allen White, Cameron Monaghan and Steve Howey. If she can't close a deal, Showtime could choose to renew the show without her or cancel it.

In its seventh season, Shameless is a top five cable drama among total viewers, adults 18-49 as well as adults 18-34. Shameless, along with Homeland, ranks as Showtime's longest-running scripted original. They are part of a roster of hourlong shows that also includes The Affair, Billions and Ray Donovan. Set to join that roster in 2017 are Twin Peaks, Jim Carrey-produced I'm Dying Up Here, Daniel Craig starrer Purity and John Ridley's Idris Elba mini Guerrilla. This past year, Showtime bid farewell to dramas Masters of Sex, Roadies and Penny Dreadful.

Rossum has become the latest actress to demand equal pay with her male co-stars. House of Cards star Robin Wright threatened to go public if she didn't get parity with Kevin Spacey on the Netflix drama. "There are very few films or TV shows where the male, the patriarch, and the matriarch are equal. And they are in House of Cards," she said in May. "I was looking at the statistics and Claire Underwood's character was more popular than [Frank's] for a period of time. So I capitalized on it. I was like, 'You better pay me or I’m going to go public.' And they did."

Other actresses who have received parity include the stars of Modern Family, who were bumped up after the show broke out (and collected multiple awards season wins) to match Ed O'Neill, who initially was paid more because he was a name-brand TV star when the show first launched. The same is true for the cast of Friends, who all wound up earning the same after Courteney Cox initially had a bigger paycheck at the show's start given her higher profile at the time.