Riverside County supervisors Tuesday voted to place a union-backed measure to protect public-safety pensions on the November ballot.

The initiative, supported by the Riverside Sheriff's Association, qualified for the ballot last month after backers gathered enough signatures.

But supervisors said Tuesday that if approved, the measure could hinder their ability to control rising retirement costs.

The proposal would prohibit the Riverside County Board of Supervisors from changing pension benefits without a vote of the electorate and would require the county to keep the current retirement formula for public-safety employees.

The proposal, known as the Public Safety and Taxpayer Protection Act, also would safeguard the benefits for family members of officers who die in the line of duty.

Since backers gathered enough signatures to qualify the measure, supervisors had few options. They could approve the ordinance or order a financial analysis and place the issue before voters.

Supervisors received the financial report Tuesday. If approved, the measure would not completely eliminate the board's ability to make pension changes. But by requiring a vote of the electorate, it would effectively lock in existing pension benefits.

Supervisor John Benoit called that a very bad idea. Supervisor Bob Buster said the measure is "very frightening."

No one from the Riverside Sheriff's Association spoke in support of the ballot measure at Tuesday's board meeting.

The county's pension liabilities for current employees and retirees are expected to jump to $6.12 billion by June 30. About $800 million remains unfunded.

To reduce costs in the future, supervisors are exploring a second-tier pension program.

Currently, sheriff's deputies and other public-safety personnel are eligible to retire at age 50 and receive 3 percent of their salary for each year of service.

If approved, the local measure would maintain that level unless voters approve changes.

According to the financial report, creating a 3 percent at age 55 system could save the county $16 million over the next decade. A 2 percent at age 50 plan would save $33 million.

And creating a hybrid system that combines aspects of a traditional 401k retirement plan could save the county $80 million by 2020, the report concluded.

Without a second tier, the report states that the county would be forced to make reductions in wages, other benefits or even services provided to the public.

Supervisors plan a competing ballot measure that would protect benefits for family members of officers killed in the line of duty but still provide for a second-tier system. A proposal has not yet come before the board.