City Councilman Eric Garcetti, one of the candidates, said Riordan's plan would make it difficult for the city to generate the money required to pay for existing employees, as their pensions would not disappear - costly, long-term obligations that have led to bankruptcy proceedings in California cities including San Bernardino and Stockton.

"In simple terms, [the plan] costs us more," he said at a campaign stop Thursday.

City Councilwoman Jan Perry said she also opposes the plan.

"I think converting from pensions to 401(k)s is a highly risky proposition that could back money out of the general fund," she told the Times.

Riordan, a multimillionaire businessman, agreed earlier in the week to a series of debates on his proposal with the Los Angeles city police union.

"Riordan has chosen to hide behind carefully orchestrated radio talk-show appearances where no challenging or insightful questions are asked, appearances before groups where he knows his ideas won't be challenged, and well-crafted media releases that lack any pretense of substance," said, Tyler Izen, president of the L.A. Police Protective League.

Riordan has until Dec. 7 to collect approximately 265,000 signatures to put the proposal on next year's ballot.