A new lawsuit says the 11 men on Nebraska's death row cannot be executed because a voter referendum backed by Governor Pete Ricketts to overturn a 2015 repeal of capital punishment failed to restore their death sentences.

In a complaint filed on Monday, the American Civil Liberties Union of Nebraska said Ricketts exceeded his power under the state constitution by helping finance and control a petition drive that ended in November 2016 when voters reinstated the death penalty.

The ACLU asked a state judge to block executions in Nebraska, saying the governor's actions made the referendum void, and that the death penalty repeal converted the 11 defendants' sentences to life in prison.

Nebraska legislators had voted to eliminate the death penalty in May 2015. Ricketts, a Republican, quickly vetoed the measure, but was overridden.

A spokesman for Ricketts had no immediate comment.

The ACLU sued less than a month after Nebraska signaled it would to move ahead with plans to eventually execute one of the defendants.

Thirty-one U.S. states, as well as the federal government, have capital punishment, according to the nonprofit Death Penalty Information Center.

According to the complaint, Ricketts overstepped his authority when he "proposed, initiated, funded, organized, operated, and controlled" the petition drive.

It said several people who were involved had close ties to the governor, and that Ricketts and his parents, TD Ameritrade Holding Corp founder Joe Ricketts and his wife Marlene, donated $425,000, or 29 percent, of the $1.45 million raised by Nebraskans for the Death Penalty, which sponsored the drive.

Last month, Nebraska Attorney General Doug Peterson said his office was prepared to seek an execution warrant for death row defendant Jose Sandoval, which could lead to the setting of an execution date, pending possible appeals.

The state also told Sandoval that it had obtained lethal injection drugs that could be used in an execution.

Sandoval was sentenced for his role in the deaths of five people in a September 2002 bank robbery in Norfolk, Nebraska.

The ACLU sued on behalf of eight of the 11 death row defendants in the district court of Lancaster County, which includes Nebraska's capital of Lincoln. According to a footnote, the other three have not consented to be plaintiffs.

(Reporting by Jonathan Stempel in New York; Editing by Cynthia Osterman)