TRENTON - The New Jersey Supreme Court was asked Monday to decide whether it is within the bounds of the state constitution to require Garden State judges and justices to pay 9 percent more toward their pensions.

A lawyer representing the state argued that a constitutional ban on reducing judges' salaries while they are on the bench does not include compensation such as pension and health benefits.

But a lawyer for the jurists argued that the 2011 law hiking judges' mandatory pension payments from 3 percent of their salary to 12 percent, an increase to be phased in over seven years, amounts to an unlawful salary reduction.

Most of the state's judges earn $165,000 and are barred from doing outside legal work. Under the change, the judges' pension payments would cost about $15,000 more a year when fully phased in.

It is essential to judicial independence that judges remain inoculated from actions of the executive and legislative branches, said the New Jersey State Bar Association, which joined the case as a friend of the court.

The case was brought by Superior Court Judge Paul DePascale of Hudson County, who challenged pension and health benefits reforms enacted by the Democratic-controlled Legislature at Republican Gov. Christie's behest.

The legislation, which required higher pension and health insurance contributions from about 500,000 government employees, also has been challenged by unions representing police, firefighters, public workers, and teachers.

This is the first suit to reach the Supreme Court. It was fast-tracked after a lower court ruled the state could not increase judges' contributions while the case proceeded. There's no word on when the court might rule.

The court is operating with one temporary justice and a second vacancy for which no temporary judge has been assigned. Chief Justice Stuart Rabner recused himself because of previous dealings on pensions while he was chief counsel to Gov. Jon S. Corzine, so the ruling will be made by five justices instead of the complement of seven.

Former Justice Peter Verniero, who listened to nearly two hours of arguments in the gallery, acknowledged the pressure the justices will face in ruling on a judicial matter. But he said they are used to deciding high-profile, controversial cases.

"Whichever way the court decides, it will engender criticism," said Verniero, who retired from the bench five years into his first seven-year term amid a controversy over racial profiling.

The case hinges on the definition of salary. The state maintains it means earnings brought home in a paycheck. The judges say it is an employee's compensation package, including benefits.

Robert Lougy, who represented the state, argued that salary is "a set amount of money" for services and that "salary protection is enough" for judges to retain their independence.

"The state's position is plainly incorrect and plainly [in violation of] . . . the New Jersey constitution," countered Justin Walder, who represented DePascale. "It is clear that a deduction, whether it is direct or indirect, is prohibited."

In response to a volley of questions from the justices, Lougy said it was "coincidence" that earlier increases in judicial benefits were offset by corresponding pay raises.

Perhaps that was because the Legislature recognized the constitutional prohibition of reducing a sitting judge's salary, Justice Barry Albin commented.

The pension-and-health-benefits law requires government workers to pay a percentage of their health-care premiums based on salary. It requires higher pension contributions from all, with the highest percentage increase for judges.