A group that represents 18,000 employees at Los Angeles City Hall warned Tuesday it will sue if the City Council enacts a plan to roll back pension benefits and boost the retirement age to 65.

With the pension plan up for a vote Tuesday, lawyers for the Coalition of L.A. City Unions sent a letter to Mayor Antonio Villaraigosa threatening a lawsuit and warning the reductions in retirement benefits will cause "irreparable harm."

Hundreds of city employees have scheduled a morning rally at City Hall, where they plan to argue that Villaraigosa and the City Council have launched an attack on unions similar to those waged in Wisconsin, where Republican Gov. Scott Walker has battled unions for much of his first term.  "This isn't pension reform. This is pension reduction," said Bob Schoonover, president of Service Employees International Union Local 721.

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