Two major city unions said Tuesday they will launch an aggressive campaign urging the public not to sign former Mayor Richard Riordan's ballot initiative to dramatically change the city's pension system.

The Los Angeles Police Protective League, in a campaign titled Public Safety First, asks that officers and LAPD supporters not sign the petition, and that supporters visit locations where the petitions are being circulated to urge people to not sign the measure.

"If you value the job that our police officers and firefighters do, please don't sign the petition," the letter from the League's board of directors urges.

The Riordan proposal applies to the Fire and Police Pension system, the Los Angeles City Employee Retirement System and the Department of Water and Power employee pension system.

The proposal would require existing workers to pay more into their pensions. Workers hired after next July 1 and would be placed in a 401(k)-style system.

The Police Protective League said the switch to a 401(k) system would actually increase the city's retirement costs and would result in less money for public safety "because the city will not have the resources to pay for an adequate number of police officers and firefighters."

The League said there was no independent study to support Riordan's proposal.

Ian Thompson, spokesman for SEIU Local 721, said the civilian employee union is also planning a campaign against the measure.

John Schwada, a spokesman for Riordan, said the former mayor is disappointed with the effort against pension reform.

"This is something the voters should decide, not something that should be left up to the unions at City Hall or to the City Council," Schwada said. "This is something the voters ought to decide."

Riordan has said he expects to have $1 million available to collect the more than 245,000 signatures needed to qualify the measure for next year's ballot.

rick.orlov@dailynews.com

213-978-0390

twitter.com/rickorlov