Rossum, 30, stars as Fiona in the hit U.S comedy-drama, a young woman forced to take care of her family due to the inability of her drug and alcohol addicted father to provide and care for them.
According to editors at The Hollywood Reporter, MACy, 66, an Oscar nominated film actor before turning to the TV role, has always been paid more than the remainder of the cast and recently renegotiated his pay deal with executives at Warner Bros, who produce the show.
Multiple insiders tell the publication Rossum is seeking a deal which would see her paid more per episode than her castmate to return for a yet to be confirmed eighth series.
Just as in the first two series of the original British show Shameless is based on, Fiona is often the focus of episodes, picking up the pieces due to her wayward father's desertion of Fiona and her five siblings.
Rossum's reported salary demands come after another female lead in a popular U.S. TV show demanded pay parity with her male co-star, as House of Cards star Robin Wright demanded to be paid the same as co-star Kevin Spacey.
The actress, who plays Claire Underwood, the scheming wife of Spacey's MAChiavellian politician Frank Underwood in the political drama, revealed in May, "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. 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."
The finale of Shameless' seventh series is set to air on U.S. TV network Showtime for 18 December (16).