Former Los Angeles Mayor Richard Riordan on Monday abandoned his controversial planned initiative to overhaul the city’s pension system, saying the campaign couldn’t gather the required signatures by next month’s deadline.

In a statement released Monday morning from Save Los Angeles, Riordan spokesman John Schwada said the campaign would not be able to gather the 300,000-plus signatures needed by the Dec. 28 deadline to place the initiative on the May ballot.

The statement said Riordan would explore other options for pension reform.

“I ask the mayor, the City Council and union heads to work with me over the next several months to save the city from bankruptcy and drastic cuts to public services,” Riordan said in the statement.

The proposed ballot measure would have converted the city’s defined benefit plan into a defined contribution plan similar to 401 (k) plans in the private sector. It would have applied to all new city employees.

The plan met with fierce opposition from city unions, who said it was flawed. Union leaders had mounted an effort to distract and block signature gatherers from collecting signatures.

After today’s announcement, Tyler Izen, president of the Los Angeles Police Protective League said, “The proposed charter amendment would have dramatically increased the city’s required payments to the three Los Angeles pension systems by hundreds of millions of dollars.”