The estate of Superman co-creator Joe Shuster has asked the U.S. Supreme Court to overturn a ruling that bars it from reclaiming a stake in the character, arguing the artist's siblings didn't have the ability to assign his copyrights to DC Comics more than two decades ago.

As Law360 reports, the estate insists the Ninth Circuit erred in its November ruling that the family relinquished all claims to Superman in 1992 in exchange for “more than $600,000 and other benefits,” which included paying Shuster’s debts following his death earlier that year and providing his sister Jean Peavy and brother Frank Shuster with a $25,000 annual pension. In October 2012, U.S. District Judge Otis D. Wright found that the agreement invalidated a copyright-termination notice filed in 2003 by Shuster’s nephew Mark Peary.

In the petition, the estate argues -- just as it did in its unsuccessful petition for a rehearing before the Ninth Circuit's full bench -- that Peavy and Frank Shuster had no termination right to exercise in 1992, because before the 1998 Copyright Extension Act that right only extended to spouses, children and grandchildren, not siblings. Therefore, DC Comics in 1992 still held the Shuster stake assigned to the company's predecessor in 1938. The estate insists Shuster's sister and brother were merely releasing DC from future payments in exchange for the pensions, an argument echoed in Judge Sidney Runyan Thomas' dissent to the November decision.

“The court of appeals' decisions cast a pall over the ownership of billions of dollars in copyrights,” the petition states. “Other grantees, inspired by the rulings of the courts of appeals, will no doubt opt to litigate upon receiving a copyright termination notice, imposing grave costs on any author or other statutory beneficiary seeking to avail herself of the rights Congress bestowed.”

The Shuster petition follows another filed in March by the heirs of Jack Kirby, who seek Supreme Court intervention in their fight with Marvel and Disney over the copyrights to 45 properties created or co-created by the artist. The justices accept only 100 to 150 out of the more than 7,000 cases they're asked to review each year.