The judges on Iowa’s Supreme Court who ruled in favour of same-sex marriage last year face a tough battle to be retained, according to a new poll.

The poll, carried out on behalf of the state’s leading paper, the Des Moines Register, shows that 44 percent of Iowans who plan to cast a ballot in the retention election say they will vote “yes” to all three justices.

Forty percent will vote to remove all three, and 16 percent say they want to retain some.

One expert who spoke to the paper said it was “virtually unheard-of for a judge to lose a retention race” in Iowa.

J. Ann Selzer, the pollster for The Des Moines Register’s Iowa Poll said the figures suggest that “some justices, and perhaps all, will be removed. It lines up along Democrat and Republican lines pretty easily, except for low-income voters, which is typically a Democratic constituency.”

The Register’s poll of 550 likely voters, conducted by Selzer & Co. from Sept. 19-22, has a margin of error of plus or minus 4.2 percentage points.

The retention election could hinge on which side mobilises the most down-ticket voters. A Register analysis of voting records in the past two non-presidential elections shows that only 60 percent of Iowa voters answered the retention questions for justices and appeals-court judges.

Justices and judges need a simple majority of “yes” votes to stay on the bench.

Removing the justices would not undo the same-sex marriage ruling or change the way judges are selected.

However, scholars who study judge-selection practices said the removal of even one justice would shock judiciaries across the nation, embolden conservative activists and, over time, could open the door to changes in the way Iowa chooses judges.

“Those poll numbers are stunning,” said Brian T. Fitzpatrick, a Vanderbilt University associate law professor who has followed Iowa’s retention debate. “It is virtually unheard-of for a judge to lose a retention race.”

No Iowa Supreme Court justice has lost a seat since the state adopted a merit-selection and retention system in 1962. The justices have won retention with an average 75 percent support since 1998, a Register analysis of voting records shows.

The Iowa Poll results come more than a year after a unanimous Iowa Supreme Court decision that overturned the state’s one-man, one-woman marriage law and allowed same-sex couples to wed.

Bob Vander Plaats, a former Republican candidate for governor, strongly opposed the ruling and formed a campaign to unseat the three justices on the ballot: Chief Justice Marsha Ternus and Justices David Baker and Michael Streit.